RFR: JDK-8306112 Implementation of JEP 445: Unnamed Classes and Instance Main Methods (Preview) [v24]

[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 40 commits:

 - Merge branch 'master' into 8306112
 - Remove mandated flag
 - Remove trailing whitespace
 - Add main  tests for inferface/enum/record
 - Improving error recovery in presence of less important syntactic errors in top-level methods and fields.
   
   Author: Jan Lahoda <jlahoda at openjdk.org>
 - Ignore SKIPs (semicolon class declarations)
 - Allow unqualified access to unnamed class (internally visible)
 - Fix missing constructor error messages and handle inner class launching
 - Merge branch 'master' into 8306112
 - Issue warning if traditional main not used.
 - ... and 30 more: https://git.openjdk.org/jdk/compare/4aea7dab...d0189fc2

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Changes: https://git.openjdk.org/jdk/pull/13689/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13689&range=23
  Stats: 1299 lines in 31 files changed: 1134 ins; 32 del; 133 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