RFR: Merge openjdk/jdk21u-dev:master [v2]

[William Kemper]

> Merges tag jdk-21.0.6+2

William Kemper has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 38 commits:

 - Merge branch 'master' into merge-jdk-21.0.6+2
 - 8342681: TestLoadBypassesNullCheck.java fails improperly specified VM option
   
   Backport-of: 8bcd4920f1b03d0ef8e295e53557c629f05ceaa4
 - 8341235: Improve default instruction frame title in PassFailJFrame
   
   Backport-of: 4ba170c403ae85576f84dafd4a157ba0db99873f
 - 8340799: Add border inside instruction frame in PassFailJFrame
   
   Backport-of: 520060f79a3cedb8f93e6bbd0e9b2823eaabf79a
 - 8340812: LambdaForm customization via MethodHandle::updateForm is not thread safe
   
   Backport-of: 47c10694c66bc131c8a5e1572340415b8daaba08
 - 8339803: Acknowledge case insensitive unambiguous keywords in tzdata files
   
   Reviewed-by: mbaesken
   Backport-of: 35a94b769761bd923fe6db03be672f05c1a74c38
 - 8306446: java/lang/management/ThreadMXBean/Locks.java transient failures
   
   Backport-of: 4ae5a3e39b681bfd001df1483d8a6d1fce0bc7f8
 - 8333728: ubsan: shenandoahFreeSet.cpp:1347:24: runtime error: division by zero
   
   Reviewed-by: mdoerr, lucy
   Backport-of: b5575942027281166676678e2081b024ec572644
 - 8342496: C2/Shenandoah: SEGV in compiled code when running jcstress
   
   Backport-of: 680dc5d896f4f7b01b3cf800d548e32bb2ef8c81
 - 8340214: C2 compilation asserts with "no node with a side effect" in PhaseIdealLoop::try_sink_out_of_loop
   
   Backport-of: ff2f39f24018436556a8956ec55da433dc697437
 - ... and 28 more: https://git.openjdk.org/shenandoah-jdk21u/compare/c0ea97ad...c1187db1

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Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/136/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=136&range=01
  Stats: 12425 lines in 74 files changed: 11328 ins; 718 del; 379 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/136.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/136/head:pull/136

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/136