[DO NOT MERGE] Ambient music - Update for favoriting intent

Support tapping the icon to allow for directly favoriting the song. If
no favoriting intent is set, fallback to using the other PendingIntent
to open the 'now playing' music list.

Also, cleanup all legacy code that was showing ambient music inside
the indication area.

Fixes: 199879413
Test: atest AmbientIndicationServiceTest
Change-Id: If06865fb78f15d247900c717d4021e1c20b2e9cc