Add new floating action menu for Accessibility targets. (3/n)

Patch action:
Obsevers the settings key and update the corresponding status.

Cherry picked from commit ff5466d3

Bug: 173958541
Test: atest AccessibilityFloatingMenuTest AccessibilityFloatingMenuViewTest AccessibilityTargetAdapterTest
Change-Id: Ic3a499f48613519313802298ee09b1e06abf1b1d
Merged-In: Ic3a499f48613519313802298ee09b1e06abf1b1d