build(aio): display types of API const docs correctly (#23850)

Previously these docs always displayed `any` as the type
of the const export. Now the type is computed correctly from
the declared type or initializer of the constant.

PR Close #23850

aio/tools/transforms/templates/api/var.template.html

@@ -2,7 +2,7 @@
 
 {% block overview %}
   <code-example language="ts" hideCopy="true" class="no-box api-heading">
-  const {$ doc.name $}: {$ doc.symbolTypeName or 'any' $};
+  const {$ doc.name $}: {$ (doc.type | escape) or 'any' $};
   </code-example>
 {% endblock %}