RFR: 8356221: Clarify Console.charset() method description

[Naoto Sato]

Simple clarification of the `Console.charset()` method description, making explicit how the charset is applied.

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

Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/25103/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25103&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356221
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25103.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25103/head:pull/25103

PR: https://git.openjdk.org/jdk/pull/25103