Pull in and/or surface WPCS inline docs

[iandunn]

WPCS has some good documentation that's exposed with --generator=Text. It includes an explanation of an error, with examples of what to do and not do. e.g.:

> phpcs ./foo.php --standard=WordPress  --generator=Text

--------------------------------------------
| WORDPRESS CODING STANDARD: SAFE REDIRECT |
--------------------------------------------

wp_safe_redirect() should be used whenever possible to prevent open redirect vulnerabilities. One of
the main uses of an open redirect vulnerability is to make phishing attacks more credible. In this
case the user sees your (trusted) domain and might get redirected to an attacker controlled website
aimed at stealing private information.

----------------------------------------- CODE COMPARISON ------------------------------------------
| Valid: Redirect can only go to allowed         | Invalid: Unsafe redirect, can be abused.        |
| domains.                                       |                                                 |
----------------------------------------------------------------------------------------------------
| wp_safe_redirect( $location );                 | wp_redirect( $location );                       |

Some ideas we could do with that:

• include that option in our messaging to plugin authors, to make sure they know about it. that could be in the brief error reports you get without --generator=Text, and in any emails we send them, etc
• write those kinds of docs for our custom sniffs
• pull those docs into the Handbook

xref https://wordpress.slack.com/archives/C5VCTJGH3/p1619591353086600