Black screen after size or surface changes

It looks like any changes in app sizes (or screen) or orientation as seen in QTBUG-132720, QTBUG-132718 and QTBUG-132717, there's always a frame or few frames where the app has a black screen. That seems to be happening whenever QtSurface.onSurfaceChanged(). That call seems to be re-assigning the surface object whenever there's a change and that's probably what's causing this issue. Initially it looks like that shouldn't be done and assigning the surface object should only be done when it's created instead.

It's worth noting that TextureView doesn't have this black screen issue.

Make sure this still works for https://github.com/qt/qtdoc/tree/6.9/examples/demos/windowembedding.