Refactor accessibility button support detection

- Moves logic to detect devices capable of supporting the
  accessibility button into AccessibilityManager from
  SettingsLib to avoid issues with resource shifting in the
  SUW binary

Bug: 37650567
Test: Existing Robolectric / Manual
Merged-In: Ibb2aaa3c2f79570df768cfa796fa890988ef82cc
Change-Id: I83bbecdf7836ae0de32ce7d39155ac0c111a8f15
3 files changed