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
11 files changed