Use decelerating interpolator for IME PB

When an app is synchronizing it's content with the IME animation, the IME should use a decelerating interpolator for the hide animation when predictive back is used.

Bug: 399082246
Flag: EXEMPT bugfix
Test: Manual, i.e. tested the IME back animation in Instagram and Messages app.
Change-Id: Ief25e3c9a01a2e448479b6c643103be6730d0dae