feat(#AlwaysOnMagnifier)!: Support always on feature in A11y controllers

Support always on feature in
MagnificationController/AccessibilityController/AccessibilityUserState.
It would check AlwaysOnMagnificationFeatureFlag and Settings to decide
whether to enable always on feature.

If both feature flag and settings preference are true, we would enable
the always on feature in FullScreenMagnificationController. Otherwise
the feature is disabled.

Bug: 146504200
Test: manual
      atest MagnificationControllerTest
      atest AccessibilityManagerServiceTest
      atest AccessibilityUserStateTest
Change-Id: Ie0ecf6276ac2323d05ddf6b185ba34d33bc8dd7d