[UX] consistent playback behavior for music and video

currently the "play" action is handled differently in video and music related windows. This PR is applying the music behavior to videos as well. This is:
* pressing play while nothing is playing -> play selected item
* pressing play while seeking or paused -> continue playback
* (new) press play while something is playing -> play selected item

The PlayPause action is not altered in any way. So pressing PlayPause while something is playing will ofc pause. IMO requires #5244 to go in as well, so that you're able to actually pause videos again which would otherwise be not possible anymore (like it's currently the case in music section - wtf).