Composer: raise the minimum supported PHPCS version to 3.8.0

... to prevent end-users from running into trouble with the name change.

The files in the Composer `vendor/bin` will only be replaced when the `replace...` directive is found and that is only available in the 3.8.0 tag.
When the files in the Composer `vendor/bin` are not replaced, they will continue to point to the `vendor/squizlabs/php_codesniffer` directory which will no longer exist, leading to fatal "File not found" errors for end-users trying to run PHPCS/PHPCBF.

Includes updating references to the PHPCS version whenever relevant throughout the codebase.

Author: jrfnl

README.md

@@ -16,7 +16,7 @@ Go to https://docs.wpvip.com/technical-references/code-review/phpcs-report/ to l
 ## Minimal requirements
 
 * PHP 5.4+
-* [PHPCS 3.7.2+](https://github.com/PHPCSStandards/PHP_CodeSniffer/releases)
+* [PHPCS 3.8.0+](https://github.com/PHPCSStandards/PHP_CodeSniffer/releases)
 * [PHPCSUtils 1.0.8+](https://github.com/PHPCSStandards/PHPCSUtils)
 * [WPCS 3.0.0+](https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards/releases)
 * [VariableAnalysis 2.11.17+](https://github.com/sirbrillig/phpcs-variable-analysis/releases)

composer.json

@@ -20,7 +20,7 @@
 		"phpcsstandards/phpcsextra": "^1.1.0",
 		"phpcsstandards/phpcsutils": "^1.0.8",
 		"sirbrillig/phpcs-variable-analysis": "^2.11.17",
-		"phpcsstandards/php_codesniffer": "^3.7.2",
+		"phpcsstandards/php_codesniffer": "^3.8.0",
 		"wp-coding-standards/wpcs": "^3.0"
 	},
 	"require-dev": {