Port to Qt6

[diegoiast]

I am only dealing with CMake, and PRO files are legacy as Qt5. Code runs, but I cannot open external files (clicking a TXT file does nothing for example). The tray , does nothing. Menus behave properly now as Qt5 has very bad Wayland support. I am testing against Qt from debian, 6.8.3 and 6.9.0 from upstream. Not compiling with MAGIC support.

On the left, Qt5 build before the changes. On the right, Qt from debian:

IMHO the code can be made to compiler on Qt5 (the normal CMake magic - just modify at the top, Qt::Widgets works on Qt5 and Qt6). I don't see any reason to spend time on this.