RFR: 8305671: javac rejects semicolons in compilation units with no imports [v3]

[Archie L. Cobbs]

> The fix for [JDK-8027682](https://bugs.openjdk.org/browse/JDK-8027682) created a new bug in which a program like this:
> 
> package p;;
> 
> would be rejected.
> 
> This is due to the previous fix swallowing all the semicolons. Instead, in the case of semicolons followed by EOF, it needs to swallow all but the last one.

Archie L. Cobbs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Consume extra semicolons in a more straightforward way.
 - Merge branch 'master' into JDK-8305671
 - Use ToolBox and add more tests per review suggestion.
 - Allow a package declaration followed (only) by multiple commas.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13361/files
  - new: https://git.openjdk.org/jdk/pull/13361/files/0865a257..f2de70cf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13361&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13361&range=01-02

  Stats: 245340 lines in 2000 files changed: 221121 ins; 11832 del; 12387 mod
  Patch: https://git.openjdk.org/jdk/pull/13361.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13361/head:pull/13361

PR: https://git.openjdk.org/jdk/pull/13361