[lworld+vector] RFR: Merge lworld

[Jatin Bhateja]

Merge latest code from lworld into lworld+vector branch.

Best Regards,
Jatin

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Commit messages:
 - post-merge fixes.
 - Merge branch 'lworld' of http://github.com/openjdk/valhalla into merge_lworld
 - Merge jdk
 - 8296149: Start of release updates for JDK 21
 - 8297642: PhaseIdealLoop::only_has_infinite_loops must detect all loops that never lead to termination
 - 8298255: JFR provide information about dynamization of number of compiler threads
 - 8298383: JFR: GenerateJfrFiles.java lacks copyright header
 - 8298379: JFR: Some UNTIMED events only sets endTime
 - 8298129: Let checkpoint event sizes grow beyond u4 limit
 - 8297718: Make NMT free:ing protocol more granular
 - ... and 1057 more: https://git.openjdk.org/valhalla/compare/8159184e...1f749c90

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - lworld+vector: https://webrevs.openjdk.org/?repo=valhalla&pr=815&range=00.0
 - lworld: https://webrevs.openjdk.org/?repo=valhalla&pr=815&range=00.1

Changes: https://git.openjdk.org/valhalla/pull/815/files
  Stats: 415200 lines in 5582 files changed: 213641 ins; 137073 del; 64486 mod
  Patch: https://git.openjdk.org/valhalla/pull/815.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/815/head:pull/815

PR: https://git.openjdk.org/valhalla/pull/815