Use FlingOnBackAnimationCallback for predictive back

Use FlingOnBackAnimationCallback to get automatically interpolated progress and out-of-the-box support for back gesture flings.

Bug: 362938401
Test: Manual, i.e. testing launcher predictive back cases (all apps, widget-picker)
Flag: com.android.window.flags.predictive_back_timestamp_api
Change-Id: I35806dbf005eb6fce97327d26c1e75bca60c2c77