Unstash taskbar due to IME immediately when system gesture starts

This is reversing a previous change from a few years ago
(ag/16325264) because we now clip the recent apps on the bottom
during gesture nav, whereas before we left them unclipped until
you swiped up.

Flag: none
Fixes: 305977350
Test: verified visuals manually in persistent, transient, and 3
button nav; also tested interactions with All Apps

Change-Id: Ib3823a9bd9aebf923ad481c010c7e8544bcb6a4d