Migration to QT6

[pktiuk]

QT6 is mature enough to start efforts of porting AntiMicroX to it.
It is also needed for updating runtime for flatpak (see: https://github.com/flathub/io.github.antimicrox.antimicrox/issues/11)

Tasks to do:

• [x] Deal with deprecated APIs
  • [x] #318
  • [x] #425
  • [x] #426
  • [x] QStringList QString::split in common.cpp
  • [x] QRect QDesktopWidget::screenGeometry in event.cpp
  • [x] QWheelEvent::orientation()
  • [x] Remove QDesktopWidget Class link

Others

• [ ] Update CMake to handle QT6

Resources:

• https://doc.qt.io/qt-6/portingguide.html
• https://www.qt.io/blog/porting-from-qt-5-to-qt-6-using-qt5compat-library