💥 Qt6 support

[OlivierLDff]

This PR introduce some breaking change:

• Stop support for Qt5
• Not sure WASM works
• Not sure static works (ios) (I guess Qt is doing that by itself now)
• Installing only work for shared library. This is what you generally want anyway.

On the new features:

• It works with Qt6 using qt5compat module for effect
• It uses qt6 macros (that is why installation doesn't work anymore) and drop my QtGeneratorCmake dependency
• flake dev shell, to quickly get a working dev env

Thanks to #111 and #135 for the prep work