[jdk23] RFR: 8318106: Generated HTML for snippet does not always contain an id

[Chen Liang]

Please review the backport of #20136, which improves the accessibility of snippets by generating an id for them if one is not specified.

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Commit messages:
 - Backport 4166e5345283d118d76b20de579d73bd55436ea6

Changes: https://git.openjdk.org/jdk/pull/20167/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20167&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318106
  Stats: 65 lines in 7 files changed: 46 ins; 0 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/20167.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20167/head:pull/20167

PR: https://git.openjdk.org/jdk/pull/20167