[lworld] RFR: 8376512: [lworld] Value objects should consistently use System.identityHashCode

[Roger Riggs]

For value objects, the ValueObjectMethods.valueObjectHashCodeAlt uses System.identityHashCode for all referenced objects.

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Commit messages:
 - The TestCloneableValue test incorrectly tested that the hashCode of the clone should be the same as the original.
 - JDK-8376512: [lworld] Value objects should consistently use System.identityHashCode

Changes: https://git.openjdk.org/valhalla/pull/1987/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1987&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376512
  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/valhalla/pull/1987.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1987/head:pull/1987

PR: https://git.openjdk.org/valhalla/pull/1987