[flexiglass] Lock indicator shows unlocked when needed.

Before this change, the code that determines which icon the lock
indicator on the lockscreen should show was using legacy state which was
not being hydrated in Flexiglass. This CL changes it to source its state
from Flexiglass. Now the lock indication is showing the correct icon at
all times.

Test: updated existing view-model unit test (also made it deviceless and
extracted some common state setup logic to make it more readable)
Test: manually verified that the lock icon is locked when the device is
locked
Test: manually verified that the lock icon is unlocked when the device
is unlocked (using a foldable - unlock, unfold, then fold again to
switch to the lockscreen scene while unlocked)
Test: could not test with fingerprint unlock because of b/341943963
Bug: 341445974
Flag: com.android.systemui.scene_container

Change-Id: Ib46df4f5bb027e4a1a8d4582867db950e230ee53