When calling resize() from showEvent(), we'd set the full geometry
on the widget's QWindow. This resulted in the top-level window
being moved to the top-left corner, even though no other call to
move() or setGeometry() had happened before.
The solution consists on calling the proper QWindow methods depending
on whether setGeometry_sys() is called for a move, a resize or both.
Furthermore, this needs QWindow::resize() to set its position policy
to frame-exclusive. The documentation states that is already the case
and we're setting the full geometry on the platform window, so we need
to convey that bit of information.
This also solves the age-old conundrum: "### why do we have isMove as
a parameter?"
Change-Id: I2e00fd632929ade14b35ae5e6495ed1ab176d32f
Task-number: QTBUG-56277
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
b65e30c861