RFR: 8305457: Implement java.io.IO

[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

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/19112/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305457
  Stats: 664 lines in 13 files changed: 660 ins; 0 del; 4 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