Add DynamicAvailabilityPreferenceController

This is a PreferenceController that correctly handles the case of
isAvailable() changing dynamically, while the Settings page containing
the preference in question is open.

Bug: 32692748
Test: m RunSettingsRoboTests

Change-Id: I95e22bbc7bdc17bacd2bf6b82fa5b535494d5bce
2 files changed