RFR: 8348092: Shenandoah: assert(nk >= _lowest_valid_narrow_klass_id && nk <= _highest_valid_narrow_klass_id) failed: narrowKlass ID out of range (3131947710)

[William Kemper]

Restore weak roots rendezvous handshake. This is necessary to have mutators complete the LRB before the concurrent GC invalidates any oop handles that may exist in native stacks.

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Commit messages:
 - Restore weak roots rendezvous handshake

Changes: https://git.openjdk.org/jdk/pull/23604/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23604&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348092
  Stats: 19 lines in 1 file changed: 14 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/23604.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23604/head:pull/23604

PR: https://git.openjdk.org/jdk/pull/23604