KeyguardTransitionInteractor#transitionValue.

This is a function that returns a flow of all transitions in or out of
the given KeyguardState. Should be useful when a consumer cares about a
specific state but doesn't care about which other state we're move in
from or moving out to.

Bug: 274159734
Flag: N/A
Test: unit test included
Test: actively calling this from the next CL
Change-Id: Iab6a756892a388e306562eae1a18a17e32112417