[jdk21u-dev] RFR: 8334482: Shenandoah: Deadlock when safepoint is pending during nmethods iteration

[Aleksey Shipilev]

Fixes Shenandoah deadlock. There is one minor contextual difference that make the backport unclean: the existence of `ICStubVerifier` that was removed in JDK 23 with [JDK-8322630](https://bugs.openjdk.org/browse/JDK-8322630).

Additional testing:
 - [ ] Linux x86_64 server fastdebug, `all` with `-XX:+UseShenandoahGC`
 - [ ] Linux AArch64 server fastdebug, `all` with `-XX:+UseShenandoahGC`

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Commit messages:
 - Backport 2aeb12ec03944c777d617d0be48982fd225b16e7

Changes: https://git.openjdk.org/jdk21u-dev/pull/880/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=880&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334482
  Stats: 72 lines in 4 files changed: 25 ins; 33 del; 14 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/880.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/880/head:pull/880

PR: https://git.openjdk.org/jdk21u-dev/pull/880