[mat graph] Add duplicate command.

MaterialGraphProject/Assets/GraphFramework/SerializableGraph/Editor/Drawing/CopySelected.cs

             if (e.type == EventType.Used)
                 return false;
 
-            if (e.commandName != "Copy" && e.commandName != "Paste")
+            if (e.commandName != "Copy" && e.commandName != "Paste" && e.commandName != "Duplicate")
                 return false;
 
             e.Use();
             if (e.type == EventType.Used)
                 return false;
 
-            if (e.commandName != "Copy" && e.commandName != "Paste")
+            if (e.commandName != "Copy" && e.commandName != "Paste" && e.commandName != "Duplicate")
-            if (e.commandName == "Copy")
+            if (e.commandName == "Copy" || e.commandName == "Duplicate")
-            if (e.commandName == "Paste")
+            if (e.commandName == "Paste" || e.commandName == "Duplicate")
                 DoPaste(parent);
             
             e.Use();

MaterialGraphProject/Assets/GraphFramework/SerializableGraph/Editor/Drawing/DrawableNode.cs

 
         public override void Render(Rect parentRect, Canvas2D canvas)
         {
-            // some imgui elements eat key down events
-            // this is okay a lot of the time
-            // but for delete key it is not desired.
-            // if we have a delete key here
-            // just return. This allows us to get
-            // a validate / execute later on that can
-            // be handled by the graph.
-            var evt = Event.current;
-            if (evt.type == EventType.keyDown 
-                && (evt.keyCode == KeyCode.Backspace || evt.keyCode == KeyCode.Delete))
-            {
-                return;
-            }
-
-            if (evt.type == EventType.ValidateCommand || evt.type == EventType.ExecuteCommand)
-                return;
-
             Color backgroundColor = new Color(0.0f, 0.0f, 0.0f, 0.7f);
             Color selectedColor = new Color(1.0f, 0.7f, 0.0f, 0.7f);
             EditorGUI.DrawRect(new Rect(0, 0, scale.x, scale.y), m_Node.hasError ? Color.red : selected ? selectedColor : backgroundColor);