Pre-release 3.5.0 rc1

This is a pre-release for version 3.5.0, which will support Qt 5.15 and Qt 6.

The generator has been adapted to be able to produce code for these versions, and to generate stable output.
The PythonQt library should be able to work with Qt 5 and 6 if compiled using these versions.
No generated sources are added for these versions. If needed, they may be added before the release.

Please test the version for your use cases, so that any fixes can be incorporated before the release (which is planned somewhere at the beginning of 2024). You can discuss the release in the associated discussion issue.