Qt5 EOL - migrate to Qt6.5

[raspher]

see Extended lifetime for Qt 5.15

[Benitoite]

see Extended lifetime for Qt 5.15

That may have been relevant to commercial qt products, however, free qt5 doesn't compile on Mac arm64, whereas qt6 does support the platform.

[CarVac]

I'm trying to work on this. A while back when Qt 6 was in beta I got it running on that, so it shouldn't take too much.

Now I just need to figure out how to convert the cmake build from 5 to 6.