Add undo actions for blackboard

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Blackboard/BlackboardField.cs

             activeFieldInfo.SetValue(m_SelectionDropper, false);
             this.AddManipulator(m_SelectionDropper);
 
-            var contextualMenuManipulator = (IManipulator)Activator.CreateInstance(s_ContextualMenuManipulator, (Action<ContextualMenuPopulateEvent>)BuildContextualMenu);
-            this.AddManipulator(contextualMenuManipulator);
+            this.AddManipulator((IManipulator)Activator.CreateInstance(s_ContextualMenuManipulator, (Action<ContextualMenuPopulateEvent>)BuildContextualMenu));
         }
 
         void BuildContextualMenu(ContextualMenuPopulateEvent evt)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Blackboard/BlackboardProvider.cs

             var property = visualElement.userData as IShaderProperty;
             if (property == null)
                 return;
+            m_Graph.owner.RegisterCompleteObjectUndo("Move Property");
             m_Graph.MoveShaderProperty(property, newIndex);
         }
 
             var property = (IShaderProperty)field.userData;
             if (newText != property.displayName)
             {
+                m_Graph.owner.RegisterCompleteObjectUndo("Edit Property Name");
                 property.displayName = newText;
                 field.text = newText;
                 DirtyNodes();
             {
                 field.RenameGo();
                 row.expanded = true;
+                m_Graph.owner.RegisterCompleteObjectUndo("Create Property");
                 m_Graph.AddShaderProperty(property);
             }
         }