RFR: 8344706: Implement JEP 512: Compact Source Files and Instance Main Methods [v8]

[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 incrementally with one additional commit since the last revision:

  Updating copyright year.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24438/files
  - new: https://git.openjdk.org/jdk/pull/24438/files/3868019e..5d0a867f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24438&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24438&range=06-07

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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