RFR: 8305457: Implement java.io.IO [v4]

[Pavel Rappo]

> Please review this PR which introduces the `java.io.IO` top-level class and three methods to `java.io.Console` for [Implicitly Declared Classes and Instance Main Methods (Third Preview)].
> 
> This PR has been obtained as `git merge --squash` of a now obsolete [draft PR].
> 
> [Implicitly Declared Classes and Instance Main Methods (Third Preview)]: https://bugs.openjdk.org/browse/JDK-8323335
> [draft PR]: https://github.com/openjdk/jdk/pull/18921

Pavel Rappo has updated the pull request incrementally with two additional commits since the last revision:

 - Specify charset of java.io.IO
 - Use system-dependent line separator for Console.println

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19112/files
  - new: https://git.openjdk.org/jdk/pull/19112/files/73a20a7c..80eacf8c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=02-03

  Stats: 5 lines in 2 files changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19112.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19112/head:pull/19112

PR: https://git.openjdk.org/jdk/pull/19112