Disable velocity-slowdown when timestamp API is enabled

When the timestamp API is enabled, apps should calculate and handle the velocity themselves. Therefore the velocity-slowdown logic is disabled.

if we would keep playing the slow-down, the velocity would always be 0 when apps receive onBackInvoked.

Bug: 362938401
Test: Manual, i.e. verify that velocity-slow down is not played anymore but onBackInvoked is called immediately when the back gesture is released.
Flag: com.android.window.flags.predictive_back_timestamp_api
Change-Id: I426ba2a8294961849f189b21a843e6622b014586