ActivityManagerService: Add method to set media fgs active.

Changes adds
-  New method in activity manager service to set
   foreground service of type media playback active. This method
   is expected to be called from MediaSessionService when media session
   is "user-engaged" from "user-disengaged" state. This method will move
   service to foreground.
-  New command in am
   am set-media-foreground-service inactive [--user USER_ID] <PACKAGE> <NOTIFICATION_ID>
   Notification ID associated with media service can be found out
   using 'dumpsys activity services` and looking for foregrondId.

Flag: com.android.media.flags.enable_notifying_activity_manager_with_media_session_status_change
BUG: 281762171
Test: atest cts/tests/app/src/android/app/cts/ActivityManagerNotifyMediaFGSTypeTest.java
Change-Id: If4c31c9ecae9bda0c1731dab0cc13d88e1225e1a
Signed-off-by: Pradeep Sawlani <sawlani@google.com>