[master] RFR: Merge jdk:jdk-21+4 [v2]

[Roman Kennke]

> Let's merge latest jdk21 tag.

Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 69 commits:

 - Merge tag 'jdk-21+4' into merge-jdk21+4
   
   Added tag jdk-21+4 for changeset 3b374c01
 - 8299594: [Lilliput] Revert "Replace stack-locking with fast-locking"
   
   Reviewed-by: shade
 - Replace stack-locking with fast-locking
   
   Reviewed-by: shade, stuefe
 - Merge jdk
   
   Reviewed-by: stuefe
 - Merge jdk
   
   Reviewed-by: stuefe
 - Implement Shenandoah support
   
   Reviewed-by: zgu
 - Merge tag 'jdk-19+20' into merge-jdk-19+20
   
   Added tag jdk-19+20 for changeset 16a8ebbf
 - Relax array elements alignment
   
   Reviewed-by: stuefe
 - Merge remote-tracking branch 'jdk-upstream/master'
 - Merge remote-tracking branch 'jdk-upstream/master'
 - ... and 59 more: https://git.openjdk.org/lilliput/compare/3b374c01...515ffce7

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Changes: https://git.openjdk.org/lilliput/pull/61/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=61&range=01
  Stats: 6154 lines in 208 files changed: 4829 ins; 774 del; 551 mod
  Patch: https://git.openjdk.org/lilliput/pull/61.diff
  Fetch: git fetch https://git.openjdk.org/lilliput pull/61/head:pull/61

PR: https://git.openjdk.org/lilliput/pull/61