mediaplaylistproxymodel: update playlist indices when moving the current track
Reason for the change
Fixes playlist bugs caused when the currently playing track's index is changed (i.e. moving the current track, or moving a track over the current track)
Test plan
Added an autotest. Steps for manual testing:
- Add a few tracks to the playlist
- Start playing a track
- Move the currently playing track to the end, then to the start
- Notice how the skip forward/backward buttons correctly update
- Pause the track
- Play the track
- The same track is playing (previously app would reset to the first track in the playlist)
Bugs fixed
Edited by Jack Hill