[lworld] RFR: 8332243: Value classes implementing Cloneable

[Frederic Parain]

Allow value classes to implement the Cloneable interface.

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Commit messages:
 - Allow value classes to implement Cloneable

Changes: https://git.openjdk.org/valhalla/pull/1131/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332243
  Stats: 127 lines in 4 files changed: 97 ins; 30 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1131.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1131/head:pull/1131

PR: https://git.openjdk.org/valhalla/pull/1131