MediaRouter: Add getUniqueId to MediaRoute2Info

MediaRoute2Info.getId() could return the same id for different routes.
From this CL, users can use MediaRoute2Info.getUniqueId() to identify
routes correctly.

Bug: 142524296
Test: atest mediaroutertest
Change-Id: I25cd45c04597a51f7e2118d64ac672ff421607f6
1 file changed