Trailing comma in parameter lists

RFC: https://wiki.php.net/rfc/trailing_comma_in_parameter_list

Example:
```php
class Uri {
    private function __construct(
        ?string $scheme,
        ?string $user,
        ?string $pass,
        ?string $host,
        ?int $port,
        string $path,
        ?string $query,
        ?string $fragment, // <- comma
    ) {
        ...
    }
}
```