MediaSessionService: Detects changes media session service apps

Bug: 72613128
Test: Following tests
  - Manually uninstall and install MediaComponents test apk and verified
    that 'dumpsys media_session' is updated accordingly.
  - Manually disabled/enabled a service in the MediaComponents test apk
    and verified that 'dumpsys media_session' is updated accordingly.
  - Manually reinstalled the MediaComponents test apk and verified that
    the session service is updated only once.
  - Run all MediaComponents tests once
Change-Id: I869853a40fb81e71f0188e84711f9d4a763defe2