Revise exit codes for PHPCS and PHPCBF commands

[gsherwood]

Version 4 is a good time to review the exit codes that both scripts produce to ensure that success cases all use 0 and that all failure cases have codes that make sense. Documentation in the wiki to describe the new exist codes should be an output of this work.

[jrfnl]

Loosely related open issues:

• Disable report for phpcbf #1818
• The "phpcs" doesn't use error exit code when invalid standard is given #2412 (discoverability of availability of exit code related CLI arguments)

[nelson6e65]

Param --runtime-set ignore_warnings_on_exit 1 works on phpcs, but it does not for phpcbf.

[dfelton]

Is there any documentation somewhere that lists all non 0 or 1 exit codes that exist, and the meaning of them?

Today was the first time I discovered an exit code of 3 is used for when and invalid standard is given. It'd be nice to be able to read a compiled list of what exit codes there are, and I cannot seem to find any information on the wiki on this topic.

[jrfnl]

@dfelton I think this is what you are looking for: #930 (comment)