Copied from https://gitlab.freedesktop.org//gstreamer/gst-plugins-bad/-/merge_requests/2331
Transition through READ or NULL are currently broken. This MR aims to address this. I have cleanup and fixed the NULL sate transition.
TODO:
- Figure-out why there is a miss-render on gnome-shell in NULL->PAUSE transition
- Fix READY -> PAUSE/PLAYING transition