AudioManager: add reporting of gapless playback support

Add reporting of gapless transitions in offload playback
via a new method AudioManager.getPlaybackOffloadSupport()
which replaces AudioManager.isOffloadPlaybackSupported().

Bug: 158191844
Test: make
Change-Id: I68c0e4865828d336ad8e1d18c5d2a550e2fedd1b
6 files changed