QMediaPlayer needs to provide information about when a seek actually completes

1. Configure QMediaPlayer to output to an abstract video surface
2. Open a large video and then pause. Then use setPosition() to seek to a specific time
3. Monitor the output on the abstract video surface. There is no programmatic method to determine when the seek actually has completed and the provided QVideoFrame is from the desired position

Possible solution: Add a signal that is emitted when the seek successfully completes. I believe the underlying media player in macOS can execute an optional callback once the seek completes, so this should be possible to implement