Fix flicker in predictive IME back animation

This CL fixes a flicker that appears sometimes when clicking an InputTextField while the IME is still animating away (initiated by predictive back anim). In that case the IME would flicker to fully shown for one frame before animating in from the bottom. This CL fixes that flicker.

Bug: 322836622
Flag: ACONFIG android.view.inputmethod.predictive_back_ime DISABLED
Test: atest FrameworksCoreTests:InsetsControllerTest
Test: atest FrameworksCoreTests:ImeBackAnimationControllerTest
Test: Manual, i.e. starting (predictive) IME hide animation and immediately click InputField again to show IME again -> Verify no flicker
Change-Id: I1bb8a9e42a372efb6c49aa437adbecb7d165596b