Replace @codingStandards comments with phpcs: comments

Problem/Motivation

We skip coding standards warnings in a number of files with @codingStandardsIgnoreFile.

From https://github.com/squizlabs/PHP_CodeSniffer/wiki/Advanced-Usage#ignorin...

Before PHP_CodeSniffer version 3.2.0, use // @codingStandardsIgnoreFile instead of // phpcs:ignoreFile. The @codingStandards syntax is deprecated and will be removed in PHP_CodeSniffer version 4.0.

Coder currently depends on PHPCS 3.5.6 so we can do this now prior to the next major version bump of PHPCS.

Steps to reproduce

Proposed resolution

Replace the comments as suggested.

Remaining tasks

Consider whether we should really ignore all sniffs for each file with phpcs:ignoreFile, or only disable some sniffs with phpcs:disable.

User interface changes

API changes

Data model changes

Release notes snippet