keyguard: don't skip the first listener dispatch

- Make mDispatchedKeyguardLockedState tri-state.
- Ensure we don't skip the first dispatch, as the value retrieved from
  KeyguardManager may be true if the KeyguardService is not connected
  yet. This will cause inconsistent values.

Flag: com.android.window.flags.dispatch_first_keyguard_locked_state
Test: manual
Bug: 375029840
Change-Id: I0938ed6df24f7ab87ba5aff0519a13ac75c25bc0