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

[Jim Laskey]

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

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Commit messages:
 - Clean up isPreview
 - Missing exception
 - Corrections
 - Update VM.java
 - Clean up testing
 - Update TestJavacTaskScanner.java
 - Merge branch 'master' into 8306112
 - Clean up
 - remnant import
 - Revised main method lookup
 - ... and 2 more: https://git.openjdk.org/jdk/compare/98e8616a...cfe08f33

Changes: https://git.openjdk.org/jdk/pull/13689/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13689&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306112
  Stats: 1265 lines in 29 files changed: 1111 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