Handle constructor promotion

[sirbrillig]

Constructor promotion (https://stitcher.io/blog/constructor-promotion-in-php-8) allows code like the following:

class MyDTO
{
    public function __construct(
        public string $name = 'Brent',
    ) {}
}

But this sniff will mark $name unused and it is in fact used. We'll need to handle that.

This was extracted from #226

[jrfnl]

For information on how support was implemented in PHPCS (via the File::getMethodParameters() method): squizlabs/PHP_CodeSniffer#3152

The same was already available via PHPCSUtils via FunctionDeclarations::getParameters() and the implementation in PHPCSUtils is backward compatible all the way back to PHPCS 2.6.0.
See: PHPCSStandards/PHPCSUtils#169