QmlDesigner.NodeInsatnces: Update positioner if binding is changing

Only if the expression of the binding is changing.

Change-Id: Ief702082dff0ac473c8ade6f3fc0f0cf36e017f3
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

share/qtcreator/qml/qmlpuppet/qml2puppet/instances/quickitemnodeinstance.cpp

@@ -354,6 +354,11 @@ void QuickItemNodeInstance::setPropertyBinding(const QString &name, const QStrin
         return; // states are only set by us
 
     ObjectNodeInstance::setPropertyBinding(name, expression);
+
+    refresh();
+
+    if (isInPositioner())
+        parentInstance()->refreshPositioner();
 }
 
 QVariant QuickItemNodeInstance::property(const QString &name) const