Windows QPA: don't resize fixed sized windows when changing screen

This seems to give pretty good result when EnableHighDPIScaling is NOT set.
But this seems to be worse when it's set.

Task-number: QTBUG-58959
Change-Id: I8de5a6c3c8b6146b1cb8f89676463206af404083
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>