The `dealerdirect/phpcodesniffer-composer-installer` Composer plugin is used to register external PHPCS standards with PHPCS.

As of Composer 2.2.0, Composer plugins need to be explicitly allowed to run. This adds the necessary configuration for that.

Refs:
* https://blog.packagist.com/composer-2-2/#more-secure-plugin-execution

Adding `--no-interaction` to "plain" Composer commands to potentially prevent CI hanging if, for whatever reason, interaction would be needed in the future.

…hpcs-plugin

Composer: allow the PHPCS plugin

…er-no-interaction

GH Actions: always use --no-interaction for Composer

WP 5.9 contains polyfills for five new PHP native functions:
* `array_key_first()` and `array_key_last()`, which were both introduced in PHP 7.3.
* `str_contains()`, `str_starts_with()` and `str_ends_with()`, which were introduced in PHP 8.0.

While the PHP 8.0 functions are not yet flagged by the latest release of PHPCompatibility, they will be once PHPCompatibility 10.0 comes out.

As `exclude`-ing error codes which don't exist yet does not lead to errors in PHPCS, we may as well add the exclusions for all WP 5.9 polyfills in one go.

Refs:
* https://core.trac.wordpress.org/changeset/52038
* https://core.trac.wordpress.org/changeset/52039
* https://core.trac.wordpress.org/changeset/52040
* https://core.trac.wordpress.org/browser/trunk/src/wp-includes/compat.php#L398-L479

Using the `dealerdirect/phpcodesniffer-composer-installer` Composer plugin is recommended to register external PHPCS standards with PHPCS.

As of Composer 2.2.0, Composer plugins need to be explicitly allowed to run.

This commit adds the CLI command to set those permissions to the installation instructions.

Includes removing a few redundant `composer install`s.

Refs:
* https://blog.packagist.com/composer-2-2/#more-secure-plugin-execution

…r-composer-2.2

README: update for Composer 2.2

WP 5.9: account for new function polyfills

Changelog for the release of version 2.1.3