Show all nav buttons when IME showing

* Keep home and recents button, and rotate back button
to be down when IME shows in 3 button task bar.
* Move IME switcher to left side of taskbar for 3 button,
keep on right side for gesture nav.

Bug: 191399224
Test: Tested RTL and LTR, gesture + button nav
with and w/o IME.

Change-Id: I7959d26986e546596e2436b8b5eb7668f44b55cf