DataTransferItem should be a class with a non-public constructor

Co-authored-by: Arman Bilge <armanbilge@gmail.com>

Author: zetashift

dom/src/main/scala/org/scalajs/dom/DataTransferItem.scala

@@ -10,7 +10,7 @@ import scala.scalajs.js
 
 /** Each DataTransferItem object is associated with a [[DataTransfer]] object. */
 @js.native
-trait DataTransferItem extends js.Object {
+class DataTransferItem private[this] extends js.Object {
 
   /** Returns the drag data item kind, one of: "string", "file". */
   def kind: DragDataItemKind = js.native