RFR: 8346667: Doccheck: warning about missing </span> before <h2>

[Nizar Benalla]

Please review this doc-only patch to avoid some unwanted failures in our HTML checks. 

Javadoc wraps everything under `@param` in a `<span>`, so having an `h2` tag there trips some of our tests that use html validators (html-tidy and some other tests). I believe you shouldn't have an `<h2>` inside of a span.

This patch tries to replace the `h2` while keeping the exact same look. The only difference is that `Value-based classes and identity operations Link icon` no longer appears in the toc on the left, which didn't look right.

This will need to be backported to JDK 24.

TIA.

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Commit messages:
 - replace use of h2 with inline css, trying to get almost the same look

Changes: https://git.openjdk.org/jdk/pull/22833/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22833&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346667
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22833.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22833/head:pull/22833

PR: https://git.openjdk.org/jdk/pull/22833