Minor codestyle clean-up

MaterialGraphProject/Assets/GraphFramework/SerializableGraph/Editor/Drawing/Drawer/HeaderDrawer.cs

             m_ExpandButton = new VisualElement
             {
                 name = "expandButton",
-                content = new GUIContent("teeest")
+                content = new GUIContent("")
             };
             var clickable = new Clickable(OnExpandClick);
             m_ExpandButton.AddManipulator(clickable);

MaterialGraphProject/Assets/GraphFramework/SerializableGraph/Editor/Drawing/Drawer/NodeDrawer.cs

     {
         protected VisualContainer m_LeftContainer;
         protected VisualContainer m_RightContainer;
-        HeaderDrawer m_HeaderDrawer;
-        VisualContainer m_InputContainer;
-        VisualContainer m_OutputContainer;
-        List<AnchorDrawData> m_CurrentAnchors;
-        VisualContainer m_ControlsContainer;
-        List<ControlDrawData> m_CurrentControlDrawData;
-        bool m_CurrentExpanded;
+        private HeaderDrawer m_HeaderDrawer;
+        private VisualContainer m_InputContainer;
+        private VisualContainer m_OutputContainer;
+        private List<AnchorDrawData> m_CurrentAnchors;
+        private VisualContainer m_ControlsContainer;
+        private List<ControlDrawData> m_CurrentControlDrawData;
+        private bool m_CurrentExpanded;
 
         public NodeDrawer()
         {
             m_LeftContainer = new VisualContainer
             {
                 classList = new ClassList("pane", "left"),
+                pickingMode = PickingMode.Ignore
             };
             {
                 m_HeaderDrawer = new HeaderDrawer();