Make MediaRoute2Info#getOriginalId() as @TestApi

This is for clearer CTS tests.

Bug: 148582813
Test: atest android.media.cts.MediaRoute2InfoTest
      atest android.media.cts.MediaRouter2Test
      atest android.media.cts.RouteDiscoveryPreferenceTest
      atest android.media.cts.RoutingSessionInfoTest
Change-Id: I6c62236d7e61a130e15b0782923b3a2f721b117d
2 files changed