RFR: JDK-8306112 Implementation of JEP 445: Flexible Main Methods and Anonymous Main Classes (Preview) [v3]

[Jim Laskey]

> Add flexible main methods and anonymous main classes to the Java language.

Jim Laskey has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 14 commits:

 - Merge branch 'master' into 8306112
 - PreviewFeatures.isEnabled()
 - Clean up isPreview
 - Missing exception
 - Corrections
 - Update VM.java
 - Clean up testing
 - Update TestJavacTaskScanner.java
 - Merge branch 'master' into 8306112
 - Clean up
 - ... and 4 more: https://git.openjdk.org/jdk/compare/96cdf93b...53a5321d

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Changes: https://git.openjdk.org/jdk/pull/13689/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13689&range=02
  Stats: 1240 lines in 29 files changed: 1086 ins; 62 del; 92 mod
  Patch: https://git.openjdk.org/jdk/pull/13689.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13689/head:pull/13689

PR: https://git.openjdk.org/jdk/pull/13689