Add tests for new MediaRouter2 scanning APIs The three `MediaRouter2DeviceTest` files correspond to different combination of router instances + permissions: 1. Local router instance 2. Proxy router instance + MEDIA_CONTENT_CONTROL 3. Proxy router instance + MEDIA_ROUTING_CONTROL Bug: 281072508 Test: atest CtsMediaBetterTogeterTestCases Change-Id: I6c418f70342ec72d5180e91ad81979601614d7eb