<i18n dev> RFR: 8354343: Hardening of Currency tests for not yet defined future ISO 4217 currency

[Justin Lu]

Please review this PR which improves future currency checking for ISO 4217 currencies.

Checking for a currency that should not yet exist in the set of available currencies is already done.
It should also be explicitly checked that such a currency can not be instantiated as well via the String getter.

-------------

Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/24782/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24782&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354343
  Stats: 35 lines in 1 file changed: 34 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24782.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24782/head:pull/24782

PR: https://git.openjdk.org/jdk/pull/24782