Integrated: Merge openjdk/jdk21u-dev:master

[William Kemper]

We have 'upstream' changes in `jdk21u-dev` that are not available in `jdk21u`. This merge takes changes from `jdk21u-dev`.

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Commit messages:
 - Merge remote-tracking branch 'openjdk-21u-dev/master' into merge-jdk21u-dev-into-shenandoah-21u-master
 - Merge
 - Merge
 - 8325670: GenShen: Allow old to expand at end of each GC
 - 8326626: GenShen: Remove dead code associated with non-elastic TLABS
 - Merge
 - Merge
 - Merge
 - 8324173: GenShen: Fix error that could cause young gcs to fail when old marking is running
 - 8321816: GenShen: Provide a minimum amount of time for an old collection to run
 - ... and 13 more: https://git.openjdk.org/shenandoah-jdk21u/compare/f2a013bd...144f87c9

The merge commit only contains trivial merges, so no merge-specific webrevs have been generated.

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/30/files
  Stats: 21982 lines in 221 files changed: 19951 ins; 952 del; 1079 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/30.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/30/head:pull/30

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/30