Add support for system media route volume adjustment

Bug: b/362507305
Test: atest CtsMediaBetterTogetherTestCases:android.media.router.cts.SystemMediaRoutingTest
Flag: com.android.media.flags.enable_mirroring_in_media_router_2
Change-Id: I771c9fe20b0a062a44fa7244526074563dd5fde6
1 file changed