RFR: 8305457: Implement java.io.IO [v6]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:

 - Fix typo
 - Merge branch 'master' into 8305457-Implement-java.io.IO
 - Simplify output.exp
 - Cover null prompt in input tests
 - Make input test parametric
 - Specify behaviour in regard to null
 - Add explicit @throws IOError to IO methods
 - Specify charset of java.io.IO
 - Use system-dependent line separator for Console.println
 - Strengthen tests after 8330998
   
   https://github.com/openjdk/jdk/pull/18996 now allows us to test
   Console IO better.
 - ... and 2 more: https://git.openjdk.org/jdk/compare/36cfe706...46a7af1f

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19112/files
  - new: https://git.openjdk.org/jdk/pull/19112/files/401d8d25..46a7af1f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19112&range=04-05

  Stats: 16584 lines in 272 files changed: 8281 ins; 5856 del; 2447 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