RFR: 8331873: Improve/expand info in `New API In` on Help page.

[Jonathan Gibbons]

Please review a relatively simple update to the generated Help page, as part of the ongoing campaign to improve the documentation around the overall use of `@since` tags.

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Commit messages:
 - 8331873: Improve/expand info in `New API In` on Help page.

Changes: https://git.openjdk.org/jdk/pull/19222/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19222&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331873
  Stats: 37 lines in 3 files changed: 37 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19222.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19222/head:pull/19222

PR: https://git.openjdk.org/jdk/pull/19222