Seal/abstract/virtual everything (#6739)

Content.Shared/DragDrop/CanDragDropOnEvent.cs

@@ -7,7 +7,7 @@ namespace Content.Shared.DragDrop;
 /// Mark this event as handled to specify that the entity can be dropped on
 /// and set CanDrop to true or false, depending on whether dropping the entity onto the target is actually possible.
 /// </summary>
-public class CanDragDropOnEvent : HandledEntityEventArgs
+public sealed class CanDragDropOnEvent : HandledEntityEventArgs
 {
     /// <summary>
     ///     Entity doing the drag and drop.

Content.Shared/DragDrop/DragDropRequestEvent.cs

@@ -9,7 +9,7 @@ namespace Content.Shared.DragDrop
     /// Requests a drag / drop interaction to be performed
     /// </summary>
     [Serializable, NetSerializable]
-    public class DragDropRequestEvent : EntityEventArgs
+    public sealed class DragDropRequestEvent : EntityEventArgs
     {
         /// <summary>
         ///     Location that the entity was dropped.

Content.Shared/DragDrop/DropAttemptEvent.cs

@@ -2,7 +2,7 @@
 
 namespace Content.Shared.DragDrop
 {
-    public class DropAttemptEvent : CancellableEntityEventArgs
+    public sealed class DropAttemptEvent : CancellableEntityEventArgs
     {
         public DropAttemptEvent(EntityUid uid)
         {

Content.Shared/DragDrop/IDraggable.cs

@@ -56,6 +56,7 @@ namespace Content.Shared.DragDrop
         }
     }
 
+    [Virtual]
     public class StartDragDropEvent : HandledEntityEventArgs
     {
         /// <summary>
@@ -80,6 +81,7 @@ namespace Content.Shared.DragDrop
         }
     }
 
+    [Virtual]
     public class CanDropEvent : StartDragDropEvent
     {
         /// <summary>
@@ -100,6 +102,7 @@ namespace Content.Shared.DragDrop
         }
     }
 
+    [Virtual]
     public class DragDropEvent : CanDropEvent
     {
         /// <summary>