When using QMouseEvent::pos to change the position of a widget, the
widget may shift in a shaking motion. This is warned about in its
documentation. For example if the system has a bit of load, we might
receive multiple mouse move events from the OS, before QMdiSubWindow
gets the first move event. In that case the first mouse move is ok,
but subsequent move events, will use a ::pos value that now does not
make sense as the position of the window have changed. The fix is to
use QMouseEvent::globalPos.
Fixes: QTBUG-72646
Change-Id: I3211cc6627ff8fe26c9520ad0457872f01c32471
Reviewed-by: Andre de la Rocha <andre.rocha@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
8b91afe12e