Use TaskFragment bounds instead of TaskBounds for Activity animation

The animation bounds is used as the RemoteAnimationTarget#localBounds.
It should be the TaskFragment bounds instead of Task bounds because the
Activity may not fill the Task when it is in a TaskFragment.

Also clean up ROOT_TASK_CLIP_BEFORE_ANIM which has no more use case.

Bug: 196173550
Test: test with demo app
Test: atest WmTests:ActivityRecordTests
Change-Id: Iff58afdb0bbae95d3f6a5756de06c0d2dfff7c88