Set animation layer for SurfaceFreezer leash

Before, when #onAnimationLeashCreated is called, it will set layer
through SurfaceAnimator. However, that doesn't cover the case when the
layer is created by the SurfaceFreezer, and has not been taken by the
SurfaceAnimator.

Bug: 196173550
Test: atest WmTests:WindowContainerTests#testAssignAnimationLayer
Change-Id: Ia3cc0eca3550e29fee00fafa8ddf356d00512df7