DO NOT MERGE Spring controlled back progress API

This CL introduces BackProgressAnimator which runs in app's main thread.
It receives target progress values from SysUI and drives the actual
progress value passed to the app with a high stiffness, no bounce
spring.

Bug: 238475284
Test: atest WindowOnBackDispatcherTest
Test: atest BackAnimationControllerTest
Test: atest TouchTrackerTest

Change-Id: Ib0d3ebe43929c405b10681000fb4e7ef8bccce34