It takes a qml scene description and renders it using a possible input
stream.
Currently supported on GLX and WGL.
Follow up to (as that MR had an old version of the commit):
- https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/475
- 4778d7166a02caf793df4f845dc35b6933d87c81: qt: add a qml overlay filter element