Ensures Accessibility button always overrides IME switcher

In the case of both the IME switcher and Accessibility button
appearing within NavigationBarView, we want to allow the
accessibility button to always override the appearance of the IME
switcher as our target users will most-often be using
dead-reckoning to interact with the Accessibility button,
requiring consistent appearance, location, and visibility.

Bug: 35267032
Test: Manual
Change-Id: Ib39d2336efe7073f686d94b3f71fc853af3186bb