ActivityManagerService: Add method to set media fgs inactive.

Changes adds a new method in activity manager service to set
foreground service of type media playback inactive. This method
is expected to be called from MediaSessionService when media session
is "user-disengaged" for certain amount of time (>10mins).
This method will move foreground service to background and allowing
application to be subject to other system policies to save resources.

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: If4e60dabeec6cc595703c0d07369d7526fe8d862