[jdk21u-dev] RFR: 8328107: Shenandoah/C2: TestVerifyLoopOptimizations test failure

[Satyen Subramaniam]

Backporting JDK-8328107: Shenandoah/C2: TestVerifyLoopOptimizations test failure. Addresses failure found when running `compiler/loopopts/TestVerifyLoopOptimizations.java` test with Shenandoah GC. Fix replaces CountedLoop with a Loop node when a load barrier is expanded on the backedge of the counted loop. Adds test to confirm expected behavior. Ran GHA Sanity Checks, local Tier 1 and 2 tests. Patch is clean.

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Commit messages:
 - Backport b5212d7bfe78b18c18e45c42c724a22365709328

Changes: https://git.openjdk.org/jdk21u-dev/pull/1616/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1616&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328107
  Stats: 92 lines in 2 files changed: 92 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1616.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1616/head:pull/1616

PR: https://git.openjdk.org/jdk21u-dev/pull/1616