Rather than mocking the PreferenceScreen's getPreference function,
a PreferenceManager has been created, which instantiates the Screen.
The desired Preference is added to the Screen with the testing key.
Rather than using a shadow XML, contexts' resources are mocked.
A mock WifiManager is used instead of a shadow
Duplicate test case removed, and test which succeeds locally but
not on cuttlefish marked as ignored for now.
Bug: 175389659
Test: atest -c DeviceNamePreferenceControllerTest
Change-Id: I643b22993a1d102614fed1883af7f4925947be20
6625f03eca