Add all missing MPRIS properties in the media session control
Summary
We are sending a lot more properties in the Desktop MPRIS plugin, so we should do the same from Android. This also paves a path toward a real MPRIS service using these properties.
I also simplified some code, making it more robust in the process.
Testing
Enable the plugin, and test the new actions (Play, Pause, Stop) from DBus. The new (better) property code can be tested using the Android debugger.
I tested using LineageOS's music player, where this all works fine. A potential issue is that not all media sessions set the play/pause/etc. possible actions properly, so more testing is needed for a few common players (e.g. Spotify).