RFR: 8305457: Implement java.io.IO [v7]

[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 one additional commit since the last revision:

  Fix System.console().readln(null) in jshell
  
  Without it, jshell hangs on me. Will think of a test.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19112/files
  - new: https://git.openjdk.org/jdk/pull/19112/files/46a7af1f..1bf7a4cd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=05-06

  Stats: 1 line in 1 file changed: 0 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