<i18n dev> RFR: 8343236: Use @apiNote and @implNote in j.util.Currency

[Justin Lu]

Please review this PR which aims to improve the _j.util.Currency_ specification by using `@apiNote` and `@implNote`.

A corresponding CSR has been filed.

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/21793/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21793&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343236
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/21793.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21793/head:pull/21793

PR: https://git.openjdk.org/jdk/pull/21793