RFR: 8341631: JShell should auto-import java.io.IO.*

[Jan Lahoda]

Adding `import static java.io.IO.*;` to the preview-default script of JShell. Also fixing JShell's console to handle the new `IO` methods properly.

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Commit messages:
 - Cleanup.
 - Fixing readln.
 - Post merge fixes.
 - Merge branch 'master' into JDK-8341631
 - Merge branch 'JDK-8342936-readln' into JDK-8341631
 - Fixing test for Console.readln/readLine, ensuring the proper methods are called.
 - Removing incorrect sentence about writing a prompt for the prompt-less readln method.
 - Adding support for IO.readln()
 - 8342936: Enhance java.io.IO with parameter-less println()
 - Fixing handling of Console input.
 - ... and 1 more: https://git.openjdk.org/jdk/compare/76a55c3c...9b6de872

Changes: https://git.openjdk.org/jdk/pull/22237/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22237&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341631
  Stats: 141 lines in 7 files changed: 124 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/22237.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22237/head:pull/22237

PR: https://git.openjdk.org/jdk/pull/22237