Expose internal video surfaces

As part of making component
QGraphicsVideoItem, QVideoWidget, and QML VideoOutput support rendering using video frames.

And all of them use QAbstractVideoSurface internally.

QAbstractVideoSurface is designed to accept QVideoFrame.
These video frames are fetched from video producers, multimedia backends, like GStreamer.

Expose internal QAbstractVideoSurface from QGraphicsVideoItem, QVideoWidget, and QML VideoOutput.