TalkBack doesn't announce when a task has being closed.

Adding announceForAccessibility() in createTaskDismissAnimation()
to announce the task has being closed.

Test: Manually tested
Fix: 186744160
Change-Id: I71f57e7ba03a61b2ced7e338da4251637e89bd16

quickstep/src/com/android/quickstep/views/RecentsView.java

@@ -2740,6 +2740,8 @@ public abstract class RecentsView<ACTIVITY_TYPE extends StatefulActivity<STATE_T
             }
         }
 
+        announceForAccessibility(getResources().getString(R.string.task_view_closed));
+
         float dismissTranslationInterpolationEnd = 1;
         boolean closeGapBetweenClearAll = false;
         boolean isClearAllHidden = isClearAllHidden();