Only dispatch onMove event to BackAnimation in one place.

Decouple the BackAnimation from EdgeBackPlugin, the motion events would
be dispatched by EdgeBackGestureHandler, other back event would be
passed by Plugin.BackCallback.

Bug: 241110428
Test: switch navigation mode from gesture => 3btn => gesture, touch
screen and monitor that BackAnimationController won't receive double
onMotionEvent for the same key.
Test: enable back affordance, verify above test.
Test: atest NexusLauncherTests:com.android.quickstep.TaplTestsQuickstep

Change-Id: Ib71030ab0e4147ff04924b2c1a5dce6b460a4b97