RFR: Merge jdk20

[Jesper Wilhelmsson]

Forwardport JDK 20 -> JDK 21

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Commit messages:
 - Merge
 - 8290919: Update nroff pages in JDK 20 before RC

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.org/?repo=jdk&pr=12150&range=00.0
 - jdk20: https://webrevs.openjdk.org/?repo=jdk&pr=12150&range=00.1

Changes: https://git.openjdk.org/jdk/pull/12150/files
  Stats: 28 lines in 27 files changed: 1 ins; 0 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/12150.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12150/head:pull/12150

PR: https://git.openjdk.org/jdk/pull/12150