Includes AccessibilityMenu on handheld devices.

In FR b/261252772 we are migrating the AccessibilityMenu accessibility
service from the Android Accessibility Suite into the framework.

This APK is very small (210KB), does not run unless enabled by
the user in accessibility Settings, and uses <150MB PSS while running
per `dumpsys meminfo`.

Bug: 266591148
Test: check that A11yMenu is present in system_ext and can be enabled
      in Settings > Accessibility
Change-Id: I4da09e4f98eb56bcfb441ca1afdeff28f6d3aa31