Introduce support for the widgets' clipRect(). Right now render-to-texture widgets
in scroll areas placed close to each other result in broken (non-existent) clipping.
Similarly, stack-on-top widgets fail to clip when placed inside a scroll area.
This is now corrected and the qopenglwidget example is enhanced to utilize a scroll
area.
Task-number: QTBUG-45860
Change-Id: I859a63d61a50d64ba9e87244f83c5969dce12337
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>
78e3354083
