Add MR2ProviderService APIs to support system media routing

This API only adds the stubs. Implementation following up.

Bug: b/362507305
Test: atest CtsMediaBetterTogetherTestCases CtsMediaHostTestCasts
Flag: com.android.media.flags.enable_mirroring_in_media_router_2
Change-Id: I16b8195959dd843c34990abdfde3cc2e83370a0e