ui: add data-preview (#412)

Co-authored-by: undefined <i@undefined.moe>

packages/ui-default/templates/partials/problem_files-additional_file.html

@@ -26,7 +26,7 @@
               <input type="checkbox" data-checkbox-group="additional_file" data-checkbox-range>
             </label>
           </td>
-          <td class="col--name">
+          <td class="col--name" data-preview="additional_file">
             <a href="{{ url('problem_file_download', {pid: pdoc.docId, filename: file.name}) }}">{{ file.name }}</a>
           </td>
           <td class="col--size">{{ size(file.size) }}</td>