Draft: Migrate to PyQt6

Open Daniel Martin requested to merge ninjakiwi/openlp:migrate-to-pyqt6 into master

My attempt to port OpenLP to PyQt6.

I wanted to see what issues we might run into when we upgrade to PyQt6. This branch has the following known issues on my machine:

  • Preview displays do not work

  • Potential crash due to me missing a enum; that are now all required to be as their extended form in PyQt6. (I used a script, but it did not catch everything)

  • Multiple graphical bugs when running on wayland (which is Qt6's default on wayland environments); XWayland works fine.

    Wayland issues:

    • Title bar flickers and sometimes not visible
    • Display window does not go on designated screen
    • Window position and size does not sustain over sessions

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