Change PlaybackState#isActiveState to isActive

Rename PlaybackState#isActiveState() to #isActive()
and make it public.
This is according to API review.

This CL also includes STATE_SKIPPING_TO_QUEUE_ITEM
as an active playback state.

Bug: 184612506
Test: build successful && atest PlaybackStateTest

Change-Id: I4757038d63adc3478f19f177265ebd198fb5f424
5 files changed