Update coding style for upcoming PHP-CS-Fixer changes

Once we bump minimum PHP version, we will get newer PHP-CS-Fixer,
which will try to apply this cleanups.

(partially cherry picked from commit 648d8c605b)

Though avoid disabling `modernize_strpos` since it was only introduced in PHP-CS-Fixer 3.2.0:
https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/commit/2ca22a27c4ffb8cc46f20e7110b1dfcbb0c8c47c

Also had to disable `visibility_required` for constants since those require PHP ≥ 7.1:
https://cs.symfony.com/doc/rules/class_notation/visibility_required.html

And remove type hint from `grabArticle` since implicitly nullable types were deprecated in PHP 8.4:
https://wiki.php.net/rfc/deprecate-implicitly-nullable-types
But we cannot use explicitly nullable types, which require PHP ≥ 7.1:
https://wiki.php.net/rfc/nullable_types

Also switch code blocks to Markdown syntax to work around `phpdoc_separation`, ApiGen uses Markdown these days anyway.
(partially cherry picked from commit 9ed89bde92)

.php-cs-fixer.php

@@ -26,6 +26,10 @@ return (new PhpCsFixer\Config())
         'strict_comparison' => true,
         'strict_param' => true,
         'concat_space' => ['spacing' => 'one'],
+        // Pulled in by @Symfony, we cannot add property types until we bump PHP to ≥ 7.4
+        'no_null_property_initialization' => false,
+        // Pulled in by @Symfony with `const` but const visibility requires PHP ≥ 7.1
+        'visibility_required' => ['elements' => ['method', 'property']],
     ])
     ->setFinder($finder)
 ;