RFR: 8335637: Add explicit well-behaved expectations to Object.{toString, hashCode}

[Joe Darcy]

Make well-behaved implementation expectations of Object.{toString, hashCode} explicit.

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Commit messages:
 - JDK-8335637: Add explicit well-behaved expectations to Object.{toString, hashCode}

Changes: https://git.openjdk.org/jdk/pull/20063/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20063&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335637
  Stats: 14 lines in 1 file changed: 14 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20063.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20063/head:pull/20063

PR: https://git.openjdk.org/jdk/pull/20063