[Media ML] Add volume-related system APIs in AudioManager

Move AudioManagerInternal APIs that MediaSessionService/
MediaSessionRecord use to AudioManager and make them system APIs.

Bug: 160682430
Test: atest CtsMediaTestCases:android.media.cts.AudioManagerTest
Change-Id: Ia6b3fd4defdb3132b8e58c8f77532668a042f7cb
8 files changed