The table of contents for module, package and class pages currently only shows a single level of headings (h2) in the main description of the page. This is a relatively shallow outline of page contents. We should add another level of headings (h3). Of course this should be done for both traditional and Markdown doc comments.

An example for a page that would benefit from this change is the page for package java.util.stream:

https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/util/stream/package-summary.html