TF-1842: Trigger handleBackgroundTask when finish task on WorkObserver

(cherry picked from commit 36c2826c1d84d76fc76dda278b4d1ef33ecab2b1)

lib/main/localizations/app_localizations.dart

@@ -2946,4 +2946,11 @@ class AppLocalizations {
       name: 'openMailboxMenu'
     );
   }
+
+  String get messageHasBeenSentSuccessfully {
+    return Intl.message(
+      'Message has been sent successfully.',
+      name: 'messageHasBeenSentSuccessfully',
+    );
+  }
 }