Flexiglass: refactor StatusBarState calculation

We keep running into bugs where we forget that we're on the keyguard or
the locked shade because the deviceUnlockStatus said we were unlocked,
so centralize the calculation into the method and be aggressive about
mapping states where we're on/over the lockscreen to KEYGUARD and
LOCKED_SHADE.

Bug: 359530769
Test: presubmit
Flag: com.android.systemui.scene_container
Change-Id: I1fa8c2e51719f0ae5ef10fe5f0e0d43db3b8a441