RFR: 8264208: Console charset API

[Naoto Sato]

Please review the changes for the subject issue.  This has been suggested in a recent discussion thread for the JEP 400 [[1](https://mail.openjdk.java.net/pipermail/core-libs-dev/2021-March/075214.html)]. A CSR has also been drafted, and comments are welcome [[2](https://bugs.openjdk.java.net/browse/JDK-8264209)].

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

Commit messages:
 - 8264208: Console charset API

Changes: https://git.openjdk.java.net/jdk/pull/3419/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3419&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264208
  Stats: 202 lines in 9 files changed: 174 ins; 17 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3419.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3419/head:pull/3419

PR: https://git.openjdk.java.net/jdk/pull/3419