Refactor enableAccessibility to AccessibilityManagerService

enableAccessibility is refactored from EnableAccessibilityController to
AccessibilityManagerService. Also added are 2 methods disableAccessibility,
and isAccessibilityEnabled.

Bug: 27645255
Change-Id: I32d75ed6617b8bcf82bbee0dd5ee776f430fb386
(cherry picked from commit 84da556422d50e43eb674061cc454f331104d493)
3 files changed