Fix tooltip position for real inside QQuickWidgets

If the QQuickWidget was embedded in a complex layout, tooltip positions
would be off. Tooltip positions need to be moved by the offset of the
actual render window.

Task-number: QTBUG-39878
Change-Id: I5f923b1d1a0956aa67afa7c05d4bfec2788682a6
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Merge remote-tracking branch 'origin/5.3' into 5.4

Conflicts:
	src/controls/Private/qquicktooltip.cpp

Change-Id: I01cdc1047d0536c965fa15e52550b4e454891610
Merge "Merge remote-tracking branch 'origin/5.3' into 5.4" into refs/staging/5.4