QmlDesigner: Fix bindingeditor on macOS

Without this the dialogs do not stay on top of the application.

Change-Id: I0b0ee06cad04ed1c8fba8dceebfbe1f93f6559cb
Reviewed-by: Aleksei German <aleksei.german@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/components/bindingeditor/bindingeditordialog.cpp

@@ -45,6 +45,7 @@ BindingEditorDialog::BindingEditorDialog(QWidget *parent)
     : QDialog(parent)
 {
     setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
+    setWindowFlag(Qt::Tool, true);
     setWindowTitle(defaultTitle());
     setModal(false);