PiP: When there's an animation happening, use animator's destBounds.

mLastReportedBounds from PipTaskOrganizer only gets updated when the
animation finishes. In the time #updateMovementBounds gets called while
there's another animation happening, using the animator's destination
bounds is a better choice.

Bug: 158225582
Test: Animation happens correctly now when shelf height change event
comes in at the same time as unexpand

Change-Id: I30f67327bb2c29f1ac5eae503cfd9d66b3f91928