[flexiglass] Pick up on non-secure auth method changes.

This CL adds logic that detects and responds to authentication method
changes between None and Swipe.

These changes occur in the Settings app, outside system UI. Unlike
changes between the different secure auth methods (PIN, password,
pattern) or between a secure auth method and a non-secure auth method
(none or swipe) and vice-versa, a switch from none to swipe or from
swipe to none has no callback mechanism nor does it produce any sort of
broadcast that system UI can depend on.

The CL takes the approach of refreshing the value whenever the scene is
starting to transition to the lockscreen scene. A flow was added to
DeviceEntryInteractor/Repository that's hydrated with a value each time
isLockscreenEnabled is invoked. Logic was added to the
SceneContainerStartable to trigger the isLockscreenEnabled method each
time a transition to the lockscreen scene is started.

Fix: 353323330
Test: added integration test at the SceneContainerStartableTest level
Test: manually verified that switching between none and swipe results in
the proper behaviour on the lockscreen
Test: manually verified switching from a secure auth method into one of
the two non-secure ones and back, also making sure it results with
proper behaviour on the lockscreen
Flag: com.android.systemui.scene_container

Change-Id: I4533345ea35511dee3ec2cc833f0b2856bd42bcd