RFR: 8305671: javac rejects semicolons in compilation units with no imports [v5]

[Archie 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 Cobbs has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:

 - Merge branch 'master' into JDK-8305671
 - Merge branch 'master' into JDK-8305671
 - 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: https://git.openjdk.org/jdk/pull/13361/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13361&range=04
  Stats: 92 lines in 2 files changed: 89 ins; 2 del; 1 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