Fix pyside6-project relative paths handling and pyproject.toml migrationHEADdev

This patch fixes two existing bugs in the pyside6-project tool:

1. Relative file paths outside the project folder in the .pyproject file
e.g. files = ["../main.py"] are not handled correctly.
A ValueError is raised due to the usage of Path.relative_to
Fixed using a new function: robust_relative_to_posix()
Updated the example_project test to contain this edge case
(Suggestion: use this as a replacement for the rel_path() function
located in tools/example_gallery/main.py)

2. The migration of a .pyproject to a pyproject.toml file with existing
content is not done properly due to removing the tomlkit implementation.
Fixed by appending the [tool.pyside6-project] section (and the [project]
section too) at the end of the file
(I don't know how the tests were passing before ??)

Change-Id: Ie061c9fa172c429c8b45381bbec35ad30d01f4ee
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>

0 files changed, 0 insertions, 0 deletions