AudioManager: add test API to query VolumePolicy

Bug: 351837292
Flag: EXEMPT bugfix
Test: atest CtsMediaAudioTestCases:android.media.audio.cts.AudioManagerTest#testAdjustUnmuteNotificationInSilent
Change-Id: Ibd7b30c963a84dc63008681cc1f2d63c86e8cf9c
5 files changed