Use custom interpolator for predictive back system animations

Bug: 332512902
Flag: ACONFIG com.android.window.flags.predictive_back_system_anims TRUNKFOOD
Test: Manual, i.e. analysing screenrecordings and verify that there are no more animation jumps at the start/end of the back animation
Change-Id: I588a8a631e068c09e88c1f3c5af5d8970746c803