🍒 kcms/tablet: Fix calibration window not appearing on the correct screen

This is due to a wacky behavior in Qt. We can work around it by showing the window first, overriding the screen then going fullscreen.

Thanks to Nicolas Fella for investigating the Qt code.

(cherry picked from commit 2a3ed3ca)

Co-authored-by: Joshua Goins josh@redstrate.com