Added functionality to double click on a subgraph node to open it up in a new shader graph window

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/MaterialNodeView.cs

                 UpdateSize();
             }*/
 
+            if (node is SubGraphNode)
+            {
+                RegisterCallback<MouseDownEvent>(OnSubGraphDoubleClick);
+            }
+
+        }
+
+        void OnSubGraphDoubleClick(MouseDownEvent evt)
+        {
+            if (evt.clickCount == 2)
+            {
+                SubGraphNode subgraphNode = node as SubGraphNode;
+
+                var path = AssetDatabase.GetAssetPath(subgraphNode.subGraphAsset);
+                ShaderGraphImporterEditor.ShowGraphEditWindow(path);
+            }
         }
 
         public AbstractMaterialNode node { get; private set; }