A11yMenu fix to Settings back button and Large Button sizing

Sets up a handler for invocations of the back action
on the A11yMenu Settings page, enabling use of its back button.
Also separates sizing logic in the adapter so that the same view
does not get resized multiple times.

Bug: 298467628
Test: install APK, enable feature flag and restart A11yMenu
Change-Id: I3bed900d6d14461d88ab363fa1646ce15a049927