Always inset the IME by the extra nav bar frame height

- If the taskbar is collapsed and isn't providing full insets to the
  app, we still want the IME to be inset for the nav button that shows

Fixes: 197727397
Test: Collapse taskbar, open IME
Change-Id: I9f2367344385c9a23e2d6323637a0b2d1713b169