Fixing animating bounds regression.

- Prior to ag/1954388, we used getAnimatingBounds() to get the final target
  bounds if animating or the current otherwise, but since we needed the
  target bounds to calculate the window scale even after the animation
  completes, the clearing of mBoundsAnimationTarget was removed.

  This inadvertently broke the check in getAnimatingBounds() from ever
  returning the current bounds (as it's never empty)!  This CL fixes the
  issue, and renames the related methods to better reflect what they are
  doing going forward.

  This caused a regression when calculating and notifying SysUI of the
  movement bounds, which was never the current bounds, but the default
  bounds.  Leading the IME change to trigger the PIP to move down.

Bug: 37242422
Test: android.server.cts.ActivityManagerPinnedStackTests
Test: Source hint rect animation still works

Change-Id: I532b0928ebfeaf95e9754a0254306af6fbb35833