Audio flags: add flag for audio focus test APIs

Add flag for disabling use of test APIs for audio focus
freeze (for deflaking tests) and timing queries.

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

Sort flags in this file alphabetically.

Test: atest android.media.audio.cts.AudioFocusTest
Bug: 301713440
Change-Id: If0cfc1267c84389a6e571f8ed32988ca13400a96