Fix back callback ordering for quick back gestures in succession

Bug: 324036420
Flag: Flag: ACONFIG com.android.systemui.predictive_back_system_animations TEAMFOOD
Test: atest BackProgressAnimatorTest
Test: Manual, i.e. verifying that starting a back gesture quickly after another one is cancelled doesn't invoke callback functions in wrong order
Change-Id: Ie5ebef743f8de07032b304f8a89dff03f318426a