Reduce confusing usages of checking occluded keyguard

The KeyguardDisplayState#mOccluded state only means that there is
either a top activity which can occlude keyguard or the dream service
is showing. While checking occluded state of keyguard outside of
KeyguardController, the callers usually expect that the keyguard
is also locked.

Bug: 297188512
Test: Disable keyguard and turn off/on screen.
      - Activity with show-when-lock
        The transition type is NONE instead of KEYGUARD_OCCLUDE.
      - Activity without show-when-lock
        No error log about visibility change without a transition.

Change-Id: Ieaad9624d816866cacc5ab5e8b5176ab74219233