feat: add new interface to catch the dropped item

src/GongSolutions.WPF.DragDrop/DefaultDropHandler.cs

@@ -326,6 +326,11 @@ public virtual void Drop(IDropInfo dropInfo)
                     {
                         destinationList.Insert(insertIndex++, obj2Insert);
                     }
+
+                    if (obj2Insert is IDragItemSource dragItemSource)
+                    {
+                        dragItemSource.ItemDropped(dropInfo);
+                    }
                 }
 
                 SelectDroppedItems(dropInfo, objects2Insert);

src/GongSolutions.WPF.DragDrop/IDragItemCloneable.cs

@@ -1,5 +1,8 @@
 namespace GongSolutions.Wpf.DragDrop
 {
+    /// <summary>
+    /// Supports cloning like the ICloneable interface, which creates a new instance of a class with the same value as an existing instance.
+    /// </summary>
     public interface IDragItemCloneable
     {
         /// <summary>

src/GongSolutions.WPF.DragDrop/IDragItemSource.cs

@@ -0,0 +1,14 @@
+namespace GongSolutions.Wpf.DragDrop
+{
+    /// <summary>
+    /// Supports methods for models which can be dropped.
+    /// </summary>
+    public interface IDragItemSource
+    {
+        /// <summary>
+        /// Indicates that the item is dropped on the destination list.
+        /// </summary>
+        /// <param name="dropInfo"></param>
+        void ItemDropped(IDropInfo dropInfo);
+    }
+}