[Lazarus] Qt6 widgetset

[zeljko]

Hi all,
I've just committed Qt6 widgetset into main :)
Tested only under linux atm (win32/64 and mac users can try to build 
libQt6Pas, if something went wrong pls inform me or open an issue about 
it), lazarus ide qt6 works just fine.

libQt6Pas is based on LTS Qt6-6.2.3, so to build libQt6Pas.so.6.2.3 you 
must have installed Qt6 with minimum version 6.2.
Read lcl/interfaces/qt6/cbindings/README howto build libQt6Pas.
Printing (Printers4Lazarus) is not yet implemented, but other stuff is 
complete.
libQt6Pas does not depend on qtnetwork anymore, it's removed since fpc 
have complete network solution.

Bug reports are welcome :)

zeljko