Implement stubs in status bar service

The new methods are not meaningful for the status bar, we're not tracking shown messages and the status bar only shows text, so there's no meaningful implementation (and no need to throw)

Author: shana

src/GitHub.Exports/Services/StatusBarNotificationService.cs

@@ -22,12 +22,13 @@ public StatusBarNotificationService([Import(typeof(SVsServiceProvider))] IServic
 
         public void HideNotification(Guid guid)
         {
-            throw new NotImplementedException();
+            // status bar only shows text, this is a noop
         }
 
         public bool IsNotificationVisible(Guid guid)
         {
-            throw new NotImplementedException();
+            // it's only text, there's no way of checking
+            return false;
         }
 
         public void ShowError(string message)