[flexiglass] Hooks up real app state and logic in keyguard (2)

- Connects the lock state (device locked or unlocked) to Flexiglass to let it show the lock screen when the device becomes locked or dismiss the lock screen when the device becomes unlocked.

Bug: 280883900
Test: Unit tests still pass.
Test: manually verified that unlocking the device through the real
bouncer automatically shows the lock screen as unlocked (the lock icon
becomes unlocked) and moves to the Gone scene
Test: manually verified that locking the device by shutting off the
screen via power button click (with "instantly lock device" setting both
on and off) properly moves back to the Lockscreen scene that shows the
lock icon as locked.

Change-Id: I82a61ade9d064597466fdaee4c01fbcf18350fea