AudioManager: flag focus test APIs

Flag test APIs for audio focus
freeze (for deflaking tests) and timing queries.

Using flag com.android.media.audio.flags.focus_freeze_test_api

Test: atest android.media.audio.cts.AudioFocusTest
Bug: 301713440
Change-Id: I36a3803bf699b9b4f73232e401f61fcae0bca4c9