<i18n dev> RFR: 8364780: Ambiguity in DecimalFormatSymbols Unicode extension priority

[Justin Lu]

This PR clarifies the Unicode extension wording in the DecimalFormatSymbols class description to make apparent that the "nu" extension is supported in addition to the "rg" extension. There already exists "nu" commentary in the specification of the  Locale accepting method APIs, the main purpose of this change is to clarify the behavior when both extensions are supplied.

Note that "may" wording is intentionally used, as symbols are only overridden if the JRE implementation provides support.

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

Commit messages:
 - copyright year
 - drive-by style changes
 - init

Changes: https://git.openjdk.org/jdk/pull/26683/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26683&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364780
  Stats: 9 lines in 1 file changed: 2 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/26683.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26683/head:pull/26683

PR: https://git.openjdk.org/jdk/pull/26683