RFR: 8344706: Implement JEP 512: Compact Source Files and Instance Main Methods [v6]

[Jan Lahoda]

> This is a PR that implements JEP: Compact Source Files and Instance Main Methods. Changes include:
> - `java.io.IO` moved to `java.lang.IO`, and no longer uses `System.console()` to implement the methods (thanks to @stuart-marks)
> - `java. ... .IO` is no longer automatically imported in any compilation unit
> - the feature is finalized (i.e. no longer requires `--enable-preview`)

Jan Lahoda has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 37 commits:

 - Merge branch 'master' into finalize-concise-source-files
 - Merge remote-tracking branch 'origin/finalize-concise-source-files' into finalize-concise-source-files
 - Add clause about handling of malformed/unmappable bytes.
 - Rewrite bits about charset decoding, removing mention of "internal objects."
 - Use local variable for System.out in print().
 - Reverting test commit.
   
   This reverts commit 7047cf007cc7de937aa21e96125083ee92932692.
 - Fixing tests.
 - Updating copyright year.
 - Adding bug number to tests.
 - Fixing IO tests path
 - ... and 27 more: https://git.openjdk.org/jdk/compare/cd6f0d19...e9f931b2

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Changes: https://git.openjdk.org/jdk/pull/24438/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24438&range=05
  Stats: 1021 lines in 57 files changed: 303 ins; 585 del; 133 mod
  Patch: https://git.openjdk.org/jdk/pull/24438.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24438/head:pull/24438

PR: https://git.openjdk.org/jdk/pull/24438