[jdk8u-dev] RFR: 8201793: (ref) Reference object should not support cloning

[Poonam Bajaj]

This is a clean backport of JDK-8201793 from jdk8u-ri to jdk8u-dev.

With this change, java.lang.ref.Reference::clone method always throws CloneNotSupportedException.

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Commit messages:
 - 8201793: (ref) Reference object should not support cloning

Changes: https://git.openjdk.org/jdk8u-dev/pull/102/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=102&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8201793
  Stats: 121 lines in 2 files changed: 121 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/102.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/102/head:pull/102

PR: https://git.openjdk.org/jdk8u-dev/pull/102