Add explicit method to dismiss Keyguard

The flag is a bit clunky for most cases, and a method is more
clear.

Test: cts/hostsidetests/services/activityandwindowmanager/util/run-test
android.server.cts.KeyguardTests

Test: cts/hostsidetests/services/activityandwindowmanager/util/run-test
android.server.cts.KeyguardLockedTests

Test: runtest systemui -c
com.android.systemui.keyguard.DismissCallbackRegistryTest

Bug: 30961403
Bug: 27422134
Change-Id: I39de90c7cfecd99350a74f72cd76418e337f2b79
diff --git a/services/core/java/com/android/server/am/ActivityStackSupervisor.java b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
index 5d8d79f..b53a680 100644
--- a/services/core/java/com/android/server/am/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
@@ -4075,7 +4075,7 @@
                                     Settings.Secure.LOCK_TO_APP_EXIT_LOCKED) != 0;
                             if (mLockTaskModeState == LOCK_TASK_MODE_PINNED && shouldLockKeyguard) {
                                 mWindowManager.lockNow(null);
-                                mWindowManager.dismissKeyguard();
+                                mWindowManager.dismissKeyguard(null /* callback */);
                                 new LockPatternUtils(mService.mContext)
                                         .requireCredentialEntry(UserHandle.USER_ALL);
                             }