NodeGroups are dirtied when one of the nodes' snapgrid position changes.

Adds method to add behavior to a node when its snapgrid position changes.

Content.Server/GameObjects/Components/NodeContainer/Nodes/Node.cs

@@ -73,6 +73,10 @@ namespace Content.Server.GameObjects.Components.NodeContainer.Nodes
             }
         }
 
+        public virtual void OnSnapGridMove()
+        {
+        }
+
         public virtual void OnContainerShutdown()
         {
             _deleting = true;