Improve display of query results in isolation tests.

Previously, isolationtester displayed SQL query results using some
ad-hoc code that clearly hadn't had much effort expended on it.
Field values longer than 14 characters weren't separated from
the next field, and usually caused misalignment of the columns
too.  Also there was no visual separation of a query's result
from subsequent isolationtester output.  This made test result
files confusing and hard to read.

To improve matters, let's use libpq's PQprint() function.  Although
that's long since unused by psql, it's still plenty good enough
for the purpose here.

Like 741d7f1, back-patch to all supported branches, so that this
isn't a stumbling block for back-patching isolation test changes.

Discussion: https://postgr.es/m/582362.1623798221@sss.pgh.pa.us

Author: tglsfdc

contrib/test_decoding/expected/concurrent_ddl_dml.out

@@ -9,12 +9,16 @@ step s1_toast_insert: INSERT INTO stream_test SELECT large_val();
 step s2_ddl: CREATE TABLE stream_test2(data text);
 step s1_commit: COMMIT;
 step s1_get_stream_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
-data           
-
+data                                    
+----------------------------------------
 opening a streamed block for transaction
-streaming change for transaction
+streaming change for transaction        
 closing a streamed block for transaction
-committing streamed transaction
-?column?       
+committing streamed transaction         
+(4 rows)
+
+?column?
+--------
+stop    
+(1 row)
 
-stop           

contrib/test_decoding/expected/concurrent_stream.out

@@ -6,33 +6,45 @@ step s1w: INSERT INTO do_write DEFAULT VALUES;
 step s2init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding'); <waiting ...>
 step s1c: COMMIT;
 step s2init: <... completed>
-?column?       
+?column?
+--------
+init    
+(1 row)
 
-init           
 step s2start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
+data
+----
+(0 rows)
 
 step s1b: BEGIN ISOLATION LEVEL SERIALIZABLE;
 step s1w: INSERT INTO do_write DEFAULT VALUES;
 step s1c: COMMIT;
 step s2start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
-
-BEGIN          
+data                                        
+--------------------------------------------
+BEGIN                                       
 table public.do_write: INSERT: id[integer]:2
-COMMIT         
+COMMIT                                      
+(3 rows)
+
 step s1b: BEGIN ISOLATION LEVEL SERIALIZABLE;
 step s1w: INSERT INTO do_write DEFAULT VALUES;
 step s2start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
+data
+----
+(0 rows)
 
 step s1c: COMMIT;
 step s2start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
-
-BEGIN          
+data                                        
+--------------------------------------------
+BEGIN                                       
 table public.do_write: INSERT: id[integer]:3
-COMMIT         
-?column?       
+COMMIT                                      
+(3 rows)
+
+?column?
+--------
+stop    
+(1 row)
 
-stop           

contrib/test_decoding/expected/delayed_startup.out

@@ -2,65 +2,89 @@ Parsed test spec with 3 sessions
 
 starting permutation: s0init s0start s1begin s1sharepgclass s2begin s2sharepgclass s0w s0start s2commit s1commit
 step s0init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
-?column?       
+?column?
+--------
+init    
+(1 row)
 
-init           
 step s0start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
+data
+----
+(0 rows)
 
 step s1begin: BEGIN;
 step s1sharepgclass: SELECT count(*) > 1 FROM (SELECT * FROM pg_class FOR SHARE) s;
-?column?       
+?column?
+--------
+t       
+(1 row)
 
-t              
 step s2begin: BEGIN;
 step s2sharepgclass: SELECT count(*) > 1 FROM (SELECT * FROM pg_class FOR SHARE) s;
-?column?       
+?column?
+--------
+t       
+(1 row)
 
-t              
 step s0w: INSERT INTO do_write DEFAULT VALUES;
 step s0start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
-
-BEGIN          
+data                                        
+--------------------------------------------
+BEGIN                                       
 table public.do_write: INSERT: id[integer]:1
-COMMIT         
+COMMIT                                      
+(3 rows)
+
 step s2commit: COMMIT;
 step s1commit: COMMIT;
-?column?       
+?column?
+--------
+stop    
+(1 row)
 
-stop           
 
 starting permutation: s0init s0start s1begin s1keysharepgclass s2begin s2keysharepgclass s0alter s0w s0start s2commit s1commit
 step s0init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
-?column?       
+?column?
+--------
+init    
+(1 row)
 
-init           
 step s0start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
+data
+----
+(0 rows)
 
 step s1begin: BEGIN;
 step s1keysharepgclass: SELECT count(*) > 1 FROM (SELECT * FROM pg_class FOR KEY SHARE) s;
-?column?       
+?column?
+--------
+t       
+(1 row)
 
-t              
 step s2begin: BEGIN;
 step s2keysharepgclass: SELECT count(*) > 1 FROM (SELECT * FROM pg_class FOR KEY SHARE) s;
-?column?       
+?column?
+--------
+t       
+(1 row)
 
-t              
 step s0alter: ALTER TABLE do_write ADD column ts timestamptz;
 step s0w: INSERT INTO do_write DEFAULT VALUES;
 step s0start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
-
-BEGIN          
-COMMIT         
-BEGIN          
+data                                                                          
+------------------------------------------------------------------------------
+BEGIN                                                                         
+COMMIT                                                                        
+BEGIN                                                                         
 table public.do_write: INSERT: id[integer]:1 ts[timestamp with time zone]:null
-COMMIT         
+COMMIT                                                                        
+(5 rows)
+
 step s2commit: COMMIT;
 step s1commit: COMMIT;
-?column?       
+?column?
+--------
+stop    
+(1 row)
 
-stop           

contrib/test_decoding/expected/mxact.out

@@ -3,28 +3,38 @@ Parsed test spec with 2 sessions
 starting permutation: s0_begin s0_getxid s1_begin s1_insert s0_alter s0_commit s0_checkpoint s0_get_changes s0_get_changes s1_commit s0_vacuum s0_get_changes
 step s0_begin: BEGIN;
 step s0_getxid: SELECT pg_current_xact_id() IS NULL;
-?column?       
+?column?
+--------
+f       
+(1 row)
 
-f              
 step s1_begin: BEGIN;
 step s1_insert: INSERT INTO harvest VALUES ((1, 2, 3));
 step s0_alter: ALTER TYPE basket DROP ATTRIBUTE mangos;
 step s0_commit: COMMIT;
 step s0_checkpoint: CHECKPOINT;
 step s0_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
-data           
+data
+----
+(0 rows)
 
 step s0_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
-data           
+data
+----
+(0 rows)
 
 step s1_commit: COMMIT;
 step s0_vacuum: VACUUM pg_attribute;
 step s0_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
-data           
-
-BEGIN          
+data                                                  
+------------------------------------------------------
+BEGIN                                                 
 table public.harvest: INSERT: fruits[basket]:'(1,2,3)'
-COMMIT         
-?column?       
+COMMIT                                                
+(3 rows)
+
+?column?
+--------
+stop    
+(1 row)
 
-stop           

contrib/test_decoding/expected/oldest_xmin.out

@@ -3,50 +3,64 @@ Parsed test spec with 3 sessions
 starting permutation: s2b s2txid s1init s3b s3txid s2alter s2c s2b s2txid s3c s2c s1insert s1checkpoint s1start s1insert s1alter s1insert s1start
 step s2b: BEGIN;
 step s2txid: SELECT pg_current_xact_id() IS NULL;
-?column?       
+?column?
+--------
+f       
+(1 row)
 
-f              
 step s1init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding'); <waiting ...>
 step s3b: BEGIN;
 step s3txid: SELECT pg_current_xact_id() IS NULL;
-?column?       
+?column?
+--------
+f       
+(1 row)
 
-f              
 step s2alter: ALTER TABLE do_write ADD COLUMN addedbys2 int;
 step s2c: COMMIT;
 step s2b: BEGIN;
 step s2txid: SELECT pg_current_xact_id() IS NULL;
-?column?       
+?column?
+--------
+f       
+(1 row)
 
-f              
 step s3c: COMMIT;
 step s1init: <... completed>
-?column?       
+?column?
+--------
+init    
+(1 row)
 
-init           
 step s2c: COMMIT;
 step s1insert: INSERT INTO do_write DEFAULT VALUES;
 step s1checkpoint: CHECKPOINT;
 step s1start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
-
-BEGIN          
+data                                                                
+--------------------------------------------------------------------
+BEGIN                                                               
 table public.do_write: INSERT: id[integer]:1 addedbys2[integer]:null
-COMMIT         
+COMMIT                                                              
+(3 rows)
+
 step s1insert: INSERT INTO do_write DEFAULT VALUES;
 step s1alter: ALTER TABLE do_write ADD COLUMN addedbys1 int;
 step s1insert: INSERT INTO do_write DEFAULT VALUES;
 step s1start: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', 'false');
-data           
-
-BEGIN          
-table public.do_write: INSERT: id[integer]:2 addedbys2[integer]:null
-COMMIT         
-BEGIN          
-COMMIT         
-BEGIN          
+data                                                                                        
+--------------------------------------------------------------------------------------------
+BEGIN                                                                                       
+table public.do_write: INSERT: id[integer]:2 addedbys2[integer]:null                        
+COMMIT                                                                                      
+BEGIN                                                                                       
+COMMIT                                                                                      
+BEGIN                                                                                       
 table public.do_write: INSERT: id[integer]:3 addedbys2[integer]:null addedbys1[integer]:null
-COMMIT         
-?column?       
+COMMIT                                                                                      
+(8 rows)
+
+?column?
+--------
+stop    
+(1 row)
 
-stop