RFR: 8368328: CompactNumberFormat.clone does not produce independent instances

[Naoto Sato]

Fixing `CompactNumberFormat.clone()` to clone mutable reference objects. The bug was caused by accessing the shared objects concurrently which resulted in an illegal state on parsing. There are other reference fields that are shared, but the contents of those fields (such as prefix/suffix) are constants/read-only, so they may be shared.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/27475/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27475&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368328
  Stats: 98 lines in 2 files changed: 97 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27475.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27475/head:pull/27475

PR: https://git.openjdk.org/jdk/pull/27475