As an optimization when calculating the safe area margins for child
widgets we look at the parent hierarchy, and if we find a widget that
is in a layout, and that layout respects the widget's contents rect,
we assume the safe area margins are accounted for already.

But this relies on the widget the layout is operating on to not opt out
of the safe area margins affecting the contents rect. If it does, the
layout can't help us, and we need to fall back to computing the child
widget's safe area margins.

Task-number: QTBUG-125345
Change-Id: I2e2f7d292d2b2c3ecd2e2e95316c4d72b92db5d6
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>