Start/stop foreground service delegate for musicfx app.

- Add MusicFxHelper class.
- Add UidObserver for each MusicFx user, and send session close whenever
an application gone.
- In the case of MusicFx process not existing, do a bindService with
BIND_AUTO_CREATE flag to create the service before start foreground
service delegate.

Bug: 293204643
Bug: 265114634
Test: Testing with YTM and Spotify with MusicFx panel
Test: dumpsys activity -a
Change-Id: I58fb58a73cc6ca8f8029be3e65d55667b6613848
Merged-In: I58fb58a73cc6ca8f8029be3e65d55667b6613848