RFR: 8340183: Shenandoah: Incorrect match for clone barrier in is_gc_barrier_node

[William Kemper]

A few commits to backport together in this PR.

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Commit messages:
 - Retain support for IU mode barrrier nodes
 - 8341242: Shenandoah: LRB node is not matched as GC barrier after JDK-8340183
 - 8340183: Shenandoah: Incorrect match for clone barrier in is_gc_barrier_node

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/124/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=124&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340183
  Stats: 22 lines in 3 files changed: 7 ins; 9 del; 6 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/124.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/124/head:pull/124

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/124