windows and xcb enables SwitchableWidgetComposition meaning that widget
backing stores will fall back to the normal flush path when no render-to-texture
widgets are visible anymore in the window. This switch however can lead to
artifacts with the image of the rtt widget remaining visible until the next
full bacinkgstore sync. The safe and simple way around this is to do the
switch only in the next flush, keeping the flush where the switch is
discovered on the OpenGL-based composition path still.
Task-number: QTBUG-54241
Change-Id: I1d3f10999f69c58efa791dd724891add56949dee
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
2a7cee47e5