LibWeb: Implement the DataTransferItemList indexed getter

Author: https://github.com/trflynn89
Commit: ceb9e30d42
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1158
Reviewed-by: https://github.com/shannonbooth

Userland/Libraries/LibWeb/HTML/DataTransfer.cpp

@@ -260,6 +260,12 @@ bool DataTransfer::contains_item_with_type(DragDataStoreItem::Kind kind, String
     return false;
 }
 
+JS::NonnullGCPtr<DataTransferItem> DataTransfer::item(size_t index) const
+{
+    VERIFY(index < m_item_list.size());
+    return m_item_list[index];
+}
+
 size_t DataTransfer::length() const
 {
     if (m_associated_drag_data_store)