[flexiglass] Add a DeviceEntry module.

This module hosts business logic and state related to device entry, i.e.
 when the user successfully dismisses (or bypasses) the lockscreen. This
 is distinct from the authentication module, which is specifically
 concerned with determining a user's identity.

The names of certain state variables have changed, too:

* `isLockscreenDismissed` is now `isDeviceEntered`
* `canSwipeToDismiss` is now `canSwipeToEnter`
* `isLockscreenEnabled` is now `isInsecureLockscreenEnabled`

Bug: 301253588
Test: Existing unit tests still pass.
Test: Added new unit tests.
Test: Manually tested the 3 different bouncer auth methods, lockscreen
 bypass and swipe, and verified they still work as expected.
Change-Id: I9596513b4319eb0a9b9a25bee3a1c1726396e4ca