Handle component's enablement state changes

Bug: 339315502
Test: manual
- Navigate to Accessibility page in Settings app
- Run `adb shell pm disable <A11yService's component name>`
- Verify the Accessibility page removes the disabled A11yService from UI
Test: atest AccessibilityManagerServiceTest
Flag: EXEMPT bugfix (low risk)

Change-Id: I725c1f292041e565bffa24ce660a2f5b2179de5e