QQuickWidget thinks of itself as a toplevel window, so it cannot process
the offsets in a parent window.

Amends 41293196

.

Task-number: QTBUG-65800
Change-Id: I8c5dcb8f44a6cbdb58bcc956d8263e68d8180bec
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>