Create a sniff to safeguard that PHPCS annotations aren't being abused

[jrfnl]

As previously discussed with @moorscode, this sniff should:

1. Check that only the new PHPCS annotations are used and forbid use of the old annotations. I.e. the following will no longer be allowed:
   • @codingStandardsIgnoreFile
   • @codingStandardsIgnoreStart / @codingStandardsIgnoreEnd
   • @codingStandardsIgnoreLine
   • @codingStandardsChangeSetting
2. Detect & forbid blanket PHPCS ignores. The new annotations allow to indicate which Standard/Category/Sniff/Errorcode should be temporarily ignored/disabled.
   • Sniff/Errorcode ignore/disables will be allowed. Errorcode based ones are preferred.
   • Standard/Category ignores/disables will not be allowed.
   • File ignores will not be allowed. These should be done from within the ruleset and documented there.
3. All temporary disables should be accompanied by a (re-) enable.
4. All ignores/disables should be accompanied by a reason for the ignore/disable.

This sniff will only be able to work when PHPCS is run with --ignore-annotations as otherwise errors on annotation tokens will be, well, ignored (default behaviour).

This means a secondary PHPCS run will be added to the Travis script if & when this sniff has been added to YoastCS and a plugin upgrades to the YoastCS version which includes it. This secondary run will only check against this particular sniff.

@moorscode In your opinion, does this summarize correctly what we discussed ?

Refs:

• https://github.com/squizlabs/PHP_CodeSniffer/releases/tag/3.2.0
• https://github.com/squizlabs/PHP_CodeSniffer/wiki/Advanced-Usage#ignoring-parts-of-a-file