build(docs-infra): ensure private exported subclasses are not rendered (#40404)

Previously, only the first layer of sub-classes were filtered to remove
private exports. But on recursing down further levels these were not
filtered out.

PR Close #40404

aio/tools/transforms/templates/api/lib/descendants.html

@@ -4,7 +4,7 @@
   {% for descendant in descendants %}
     <li>
       <code>{$ descendant.name $}</code>
-      {$ renderDescendantList(descendant.descendants | filterByPropertyValue('docType', docTypeMatcher), docType, recursed, docTypeMatcher) $}
+      {$ renderDescendantList(descendant.descendants | filterByPropertyValue('docType', docTypeMatcher) | filterByPropertyValue('privateExport', undefined), docType, recursed, docTypeMatcher) $}
     </li>
   {% endfor %}
 </ul>