Update to support PHP-CS-Fixer 3.x

[owenvoke]

Is your feature request related to a problem? Please describe.
PHP-CS-Fixer 3.x has been released recently, and I was hoping to start using it.

Describe the solution you'd like
A new release with support for 3.x. 👍🏻

I've started working on the transition to the new version. I was initially going to try and get it working with the new rule names (which still work on PHP-CS-Fixer 2.x), and then eventually migrate to v3.

It looks like the issues I've hit so far are as follows:

• The Config::setRules() method now has a return type of PhpCsFixer\ConfigInterface which means that we can't cover both v2.x and v3.x with the same config class unfortunately. Unless I'm mistaken.
• class_definition is causing issues with Laravel 8, although this seems to be covered by Braces on anonymous classes #47 and is a separate issue. (resolved by ignoring that test in ci: update to test PHP 8 #48)

I've currently used .php-cs-fixer.dist.php as the config name, but I'm happy to go with .php-cs-fixer.php instead if that would be better.

Describe alternatives you've considered
N/A

Additional context
N/A

[owenvoke]

This now actually updates to use v3.x of the package, so the config has been updated to use PhpCsFixer\ConfigInterface as the return type in cd8b6e8. If you'd rather have two branches or anything to support both, then you can revert that commit on the v2.x branch. 👍🏻

[matt-allan]

Awesome, thanks so much!