Launch ConfirmDeviceCredentials on a new task stack

Fixes: 123951409
Test: Manually verified with biometricpromptdemo app.
Change-Id: I0d99a254f3e9a4da7dc329d51fe32ae6d38f75ed

services/core/java/com/android/server/biometrics/BiometricService.java

@@ -628,6 +628,9 @@ public class BiometricService extends SystemService {
                             null /* description */);
                     // Then give it the bundle to do magic behavior..
                     intent.putExtra(KeyguardManager.EXTRA_BIOMETRIC_PROMPT_BUNDLE, bundle);
+                    // Create a new task with this activity located at the root.
+                    intent.setFlags(
+                            Intent.FLAG_ACTIVITY_MULTIPLE_TASK | Intent.FLAG_ACTIVITY_NEW_DOCUMENT);
                     getContext().startActivityAsUser(intent, UserHandle.CURRENT);
                 });
                 return;