Implement ECS alternative for IDragDropOn and fully ECS disposal units (#6380)

Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>

Content.Shared/DragDrop/SharedDragDropSystem.cs

@@ -0,0 +1,15 @@
+using Robust.Shared.GameObjects;
+
+namespace Content.Shared.DragDrop;
+
+public abstract class SharedDragDropSystem : EntitySystem
+{
+    protected bool? CheckDragDropOn(DragDropEvent eventArgs)
+    {
+        var canDragDropOnEvent = new CanDragDropOnEvent(eventArgs.User, eventArgs.Dragged, eventArgs.Target);
+
+        RaiseLocalEvent(eventArgs.Target, canDragDropOnEvent, false);
+
+        return canDragDropOnEvent.Handled ? canDragDropOnEvent.CanDrop : null;
+    }
+}