Media: add onRoute*** callback

Make onRouteAdded/Changed/Removed available in
MediaRouter2Manager.Callback

Currently onRouteAdded is only included in the test.
(onRouteRemoved is not called properly due to not handling removed
providers correctly).

Bug: 130875543

Test: atest mediaroutertest w/ mediarouteprovider installed

Change-Id: Idd1fdaeb9fcf1c4b8c2b7798c3ed62eeb044d2cb