RFR: 8344049: Shenandoah: Eliminate init-update-refs safepoint

Mon Mar 24 23:28:02 UTC 2025

Not clean, has two follow up fixes in this PR.

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Commit messages:
 - Fix merge conflict
 - 8348092: Shenandoah: assert(nk >= _lowest_valid_narrow_klass_id && nk <= _highest_valid_narrow_klass_id) failed: narrowKlass ID out of range (3131947710)
 - Backport: 8c09d40d6c3
 - Backport: 764d70b7df18e288582e616c62b0d7078f1ff3aa

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/161/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=161&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344049
  Stats: 303 lines in 12 files changed: 172 ins; 84 del; 47 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/161.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/161/head:pull/161

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/161