Fix a problem that Dialog does not close in new dispatch.

We can treat Dialog as a standard widget that handles back.
Its dedicated back nav type is not in use and can eventually be removed.

Test: try dismiss dialog in BackTest app.

Change-Id: If89856ccfac8b1fd968aa674628476de02fbf489
(cherry picked from commit 6cb6399008)

core/java/android/app/Dialog.java

@@ -465,7 +465,8 @@ public class Dialog implements DialogInterface, Window.Callback,
                     onBackPressed();
                 }
             };
-            getOnBackInvokedDispatcher().registerSystemOnBackInvokedCallback(mDefaultBackCallback);
+            getOnBackInvokedDispatcher().registerOnBackInvokedCallback(
+                    mDefaultBackCallback, OnBackInvokedDispatcher.PRIORITY_DEFAULT);
             mDefaultBackCallback = null;
         }
     }