Also rename gtk_media_stream_ended to
gtk_media_stream_set_ended, to avoid naming
collision with GtkMediaStream:ended.
The existing entry points still exist, deprecated
and marked as non-introspectable.
Update all internal uses.
Fixes: #4023
Some bindings can't handle the coexistence of
GtkMediaStream:prepared and gtk_media_stream_prepared.
Help them out by renaming the function to
gtk_media_stream_set_prepared, and rename
gtk_media_stream_unprepared as well, to match.
The existing entry points still exist, deprecated.
Update all internal uses.
Fixes: #4023
