qtmir: Take screen rotation into account when calculating mouse pointer position

Requirements:

• Install Debian 13 minimal
• Install Lomiri: apt install lomiri
• Hardware requirements:
  • tablet device that rotates the screen content if the tablet device is rotated
  • external USB keyboard
  • external mouse (or combined keyboard + touchpad)

How to reproduce:

• Login into Lomiri, hold the tablet device in its default orientation
• Assure staged mode (tablet mode, i.e. all apps are full screen, launcher icon / Lomiri logo is in the bottom left corner), if needed enforce it via disabling "Computer Mode" in the System/Session indicator's menu
• open a terminal window and/or some other app
• Plugin keyboard and mouse pointing device (e.g. a combined wireless Logitech keyboard with integrated touchpad)
• Lomiri should automatically switch into windowed mode (desktop mode). If it does not do that automatically, enforce it via System/Session indicator's menu item "Computer Mode" (enable the toggle)
• Try to grab window decorations of the open app windows and try to maximize or move the windows (should work)
• Now rotate the device 180°, the shell should follow the rotation
• Try again to grab window decorations of the open app windows and try to maximize or move the windows (should not work)
• Try to imagine where the app windows would be if the screen was still rotated back 180°, try to "grab" the windows there (empty desktop space). This should work.
• Rotate the device 90° compared to its original position. Note that you can move the mouse pointer way off screen to the right now... Same problem with reaching out for controls in the window decorations

The expected fix:

• when the device and the shell is rotated and Lomiri operates in desktop mode, the mouse pointer should be usable just as if the device was not rotated.
• similarly, rotating the device by 90° or 270°, the mouse pointer should positioning should work

Hint:

• We have just reverted a patch for this which caused mouse pointer jumpings: 15db2d0a