RFR: 8325324: Implement Declared Classes and Instance main Methods

[Jan Lahoda]

This is an implementation of a change for JEP draft: Implicitly Declared Classes and Instance Main Methods (Third Preview)[1]. The primary change here is that implicitly declared classes have two new implicit imports:

import module java.base;
import static java.io.SimpleIO.*;


Both of these depend on other changes, the first one on https://github.com/openjdk/jdk/pull/18614, and the second one on https://bugs.openjdk.org/browse/JDK-8305457. This PR depends on 18614, and the patch here can should be able to work both in the presence and absence of `java.io.SimpleIO`, including testing. Some tweaking may still be necessary when `java.io.SimpleIO` is introduced. But, overall the patch should be fairly straightforward - the imports are injected at the same time the long-existing import for `java.lang` is added.

There is also an obvious relation to String Templates, which may need tweaking/simplification.

Additional tweak will be needed once the JEP is Candidate, to updated the proper JEP number.

[1] https://openjdk.org/jeps/8323335

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Depends on: https://git.openjdk.org/jdk/pull/18614

Commit messages:
 - Adding test verifying that the new implicit imports are not used for ordinary classes.
 - Merge branch 'module-imports' into JDK-8325324
 - Fixing test.
 - Merge branch 'master' into JDK-8325324
 - Disabling the preview check when working with the STR.
 - Cleanup StringTemplate.STR import.
 - Implicitly importing SimpleIO.
 - 8325324: Implement Declared Classes and Instance main Methods

Changes: https://git.openjdk.org/jdk/pull/18633/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18633&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325324
  Stats: 301 lines in 4 files changed: 275 ins; 11 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/18633.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18633/head:pull/18633

PR: https://git.openjdk.org/jdk/pull/18633