QmlJSEditor: extending IContextPane with a signal

closed() is emitted when the pane is hidden/closed.

src/libs/qmleditorwidgets/contextpanewidget.cpp

@@ -363,6 +363,7 @@ void ContextPaneWidget::onTogglePane()
         setLineButton();
     } else {
         deactivate();
+        emit closed();
     }
 }