Fix that cut-over OTA to Android T disabled magnification via nav-bar accessibility shortcut.

Root cause:
Didn’t initial the correct accessibility state when creating the navigation bar view.

Solution:
Add updateA11yState() into the init() and onAccessibilityServicesStateChanged(AccessibilityManager)

Bug: 219732138
Test: atest NavBarHelperTest
Change-Id: Idf951088cbbaacf259026aace4e7090fb9903c0e