RFR: Merge jdk20

[Jesper Wilhelmsson]

Forwardport JDK 20 -> JDK 21

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Commit messages:
 - Merge remote-tracking branch 'jdk20/master' into Merge_jdk20
 - 8298400: Virtual thread instability when stack overflows
 - 8300490: Spaces in name of MacOS Code Signing Identity are not correctly handled after JDK-8293550

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.org/?repo=jdk&pr=12103&range=00.0
 - jdk20: https://webrevs.openjdk.org/?repo=jdk&pr=12103&range=00.1

Changes: https://git.openjdk.org/jdk/pull/12103/files
  Stats: 45 lines in 6 files changed: 40 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/12103.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12103/head:pull/12103

PR: https://git.openjdk.org/jdk/pull/12103