Unit test for BubbleBarDropTargetController

Add tests to check that drop target is shown or not shown as needed.
Check that location and size are what is expected.

Refactor animating the drop target in and out in the controller. Moving
from ViewPropertyAnimator to ObjectAnimator. ObjectAnimator can be
controlled in the test with the AnimatorTestRule.

Bug: 313661121
Test: atest WMShellMultivalentTestsOnDevice:BubbleBarDropTargetControllerTest
Test: atest WMShellRobolectricTests:BubbleBarDropTargetControllerTest

Change-Id: Ia4253a8ff2e631c34b2d9dffeb1e4abfa424a439