Refine logic about controlling transient bars

- Use copied InsetsSourceControl to prevent the leash from being
  released while the control gets revoked while playing transient
  bar animations.
- Start the animation after mAnimationControl gets assigned to prevent
  NullPointerException.
- Let SystemUI to change the bar mode to transient mode before WM
  plays the transient bar animation.
- Remove a redundunt call to the super method.
- Fix InsetsPolicyTest
- Fix InsetsStateControllerTest
- Fix misc things

Bug: 118118435
Test: Manually swipe to show transient bars many times.
Test: atest InsetsSourceProviderTest InsetsStateControllerTest
            InsetsPolicyTest WindowStateTests CommandQueueTest
            RegisterStatusBarResultTest InsetsFlagsTest
            LightBarControllerTest RegisterStatusBarResultTest
            ViewRootImplTest DisplayPolicyInsetsTests
            DisplayPolicyTests TaskSnapshotSurfaceTest
            InsetsAnimationControlImplTest
Change-Id: I7d445b7dc6f47a64048937cd439bdd5ffa7fa3a3