Fix accessibility settings page did not update the preference state

Root Cause: Keys in ContentObserver registered after the keys change

Solution: Keys in ContentObserver need to be observed during the whole lifecycle to update the preferences including summary text

Fix: 183157677
Fix: 172469017
Fix: 183459237
Fix: 183459376
Test: atest AccessibilitySettingsTest
Change-Id: I3b22773965f1878c499a0f9cbd8bd0f3c9c6fae9