RFR: 8324126: Error message for mistyping -XX:+Unlock...Options is not helpful [v2]

[Sonia Zaldana Calles]

> If we run the VM option to unlock experimental vm options without the preceding ‘+’, the error message is not very helpful: 
> 
> ```Error: VM option 'UnlockExperimentalVMOptions' is experimental and must be enabled via -XX:+UnlockExperimentalVMOptions.```
> 
> With the proposed change, we should see a more descriptive error message, namely the lack of a +/- sign. 
> 
> ```Missing +/- setting for VM option 'UnlockExperimentalVMOptions'```
> 
> Testing: runtime/commandLine regression tests pass. Also added a regression test to verify expected behaviour.

Sonia Zaldana Calles has updated the pull request incrementally with two additional commits since the last revision:

 - display both error messages (locked and well-formed)
 - Sorting out copyright header errors

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17575/files
  - new: https://git.openjdk.org/jdk/pull/17575/files/b6702332..afb70cb8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17575&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17575&range=00-01

  Stats: 27 lines in 2 files changed: 11 ins; 9 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/17575.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17575/head:pull/17575

PR: https://git.openjdk.org/jdk/pull/17575