Clarify docs for Animator.isStarted()
Clarify docs for Animator.isStarted()

Behavior is different than spec'd for one-shot animators, clarified
docs to reflect that.

Issue #21087798 better docs for isStarted()

Change-Id: I499a5d52cf02ef715acb6ae0635ede4328c93de8

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base