[meta] Coding Standards in Rules 8.x

This is a meta issue for coding standards. The state as at 9 June 2022 is:

Core 9.0

PHP_CodeSniffer 3.5.5, Coder 8.3.9 - 0 messages

Core 9.1

PHP_CodeSniffer 3.5.6, Coder 8.3.9 - 0 messages

Core 9.2

PHP_CodeSniffer 3.6.0, Coder 8.3.13 - 0 messages

Core 9.3

PHP_CodeSniffer 3.6.1, Coder 8.3.13 - 0 messages

Core 9.4

PHP_CodeSniffer 3.6.2, Coder 8.3.15 - 19 messages