[flexiglass] Authentication logic.

Creates a System UI "auth" module that can handle logic surrounding
application state like device unlocked, the selected authentication
method (e.g. PIN, password, pattern), and whether bypass is enabled.
Also handles business logic like locking and unlocking the device and  making sure to automatically treat the
device as unlocked when the authentication method is "None".

Bug: 280883900
Test: Unit tests. Manual verification through testbed app.
Change-Id: I32b7b58582afda32be40b321a3e3cbd964fabcfa