Main window blinks when adding QWebEngineView into a layout

(COPY OF THE PARENT TASK, there is no access to the original author account, but the issue was not fixed)

This is a regression since Qt 6.3.2. The issue is reproducible at least on Qt 6.9.0/6.8.1/6.6.3 on Windows Server 2022/Ubuntu 22

If I create main window initially (with a raster surface by default) and later QWebEngineView is added into any layout, the main window is hidden for a short period of time. This happens only once: if I create the first QWebEngineView. The main window is not hidden anymore if other instances of QWebEngineView are created.

After some investigation I found that it happens when a widget with OpenGL surface is reparented into a main window with a raster surface. In this case the surface type changes and resources of the main window are destroyed and recreated.

The sample code is attached: webengine-bug.cpp

Additionally, the issue was reproduced using Python code (for easier testing); a README.md file is included in the archive:

QTBUG-121181.zip