Add Item#copy

api/src/main/java/com/viaversion/viaversion/api/minecraft/item/DataItem.java

@@ -92,6 +92,11 @@ public class DataItem implements Item {
         this.tag = tag;
     }
 
+    @Override
+    public Item copy() {
+        return new DataItem(identifier, amount, data, tag);
+    }
+
     @Override
     public boolean equals(final Object o) {
         if (this == o) return true;

api/src/main/java/com/viaversion/viaversion/api/minecraft/item/Item.java

@@ -87,4 +87,11 @@ public interface Item {
      * @param tag item tag
      */
     void setTag(@Nullable CompoundTag tag);
+
+    /**
+     * Returns a copy of the item.
+     *
+     * @return copy of the item
+     */
+    Item copy();
 }