MediaSession browser bugs

[Derkades]

It turns out that parts of the MediaSession API are not implemented or broken in many browsers.

Browser	Play/pause	Title/artist/album info	Next/previous	Current position	Seek	Album cover
Firefox, Linux (mpris)*	Working	Working	Working	Not implemented	Not implemented	Broken?
Chromium, Linux (mpris)*	Working	Working	Working	Working	Working	Broken?
Firefox, Windows	Working	Working	Working	?	?	Broken?
Chrome, Windows	Working	Working	Working	Working	Working	Working
Firefox, Android	Working	Not implemented	Not implemented	Not implemented	Not implemented	Not implemented
Vanadium, Android	Working	Working	Working	Working	Working	Working

* tested using playerctl, KDE media player widget, GNOME media player widget