Cmake build with qt6 on MAC

Cmake build with qt6 on MAC

Patch from P. De Visschere
Citing:
I also must exclude the QMacPasteboardMimeGraphics class in
GuiApplication.cpp since QMacPasteboard is not available anymore with qt6.

and add an #include <QStandardPaths> in support/Package.cpp (I suppose
this will pose no problem for qt5 but have not checked it, it's only
needed with USE_MACOSX_PACKAGING)