Disable IME predictive back animation in multi-window mode

In multi-window mode, the IME is controlled by DisplayImeController instead of the regular InsetsController. Therefore we must disable the InsetsController animation in that case. We should implement the animation in DisplayImeController instead for that case.

Bug: 346726115
Flag: android.view.inputmethod.predictive_back_ime
Test: Manual, i.e. verifying that no interactions happen with InsetsController, predictive animation is not played but IME dismissing works as usual in multi-window mode.
Test: atest ImeBackAnimationControllerTest
Change-Id: Iff275d7dfd1c920b246034f8dc678cd27ecacc0f