[CF 4690] v8 - Teach predtest about IS [NOT] <boolean> proofs

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/4690

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAAaqYe-s59GXnfEb-V39oBhp=W5zRDABn3Zk77vYOgZi8k+T6A@mail.gmail.com
Author(s): James Coleman

Author: Commitfest Bot