RFR: 8332124: Jcmd processing should accept the "help" sub option as command argument [v2]

[Sonia Zaldana Calles]

> Hi all, 
> 
> This PR addresses [8332124](https://bugs.openjdk.org/browse/JDK-8332124) enabling jcmd to accept "help" as an argument to subcommands. 
> 
> Testing: 
> - [x] Verified running `jcmd 4711 VM.metaspace help` works along with other subcommands. 
> - [x] Added test case passes. 
> 
> Thanks, 
> Sonia

Sonia Zaldana Calles 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 three additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8332124
 - Adding test case for suboptions with trailing spaces and adding null terminator to reordered command
 - 8332124: Jcmd processing should accept the "help" sub option as command argument

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19776/files
  - new: https://git.openjdk.org/jdk/pull/19776/files/21c10314..962b29f2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19776&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19776&range=00-01

  Stats: 355 lines in 34 files changed: 191 ins; 73 del; 91 mod
  Patch: https://git.openjdk.org/jdk/pull/19776.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19776/head:pull/19776

PR: https://git.openjdk.org/jdk/pull/19776