Default value of the $flag argument changed in PHP 8.1 from ENT_COMPAT to ENT_QUOTES | ENT_SUBSTITUTE
To ensure consistent behavior across different PHP version the second parameter is now required for the functions:
htmlspecialchars(), htmlentities(), htmlspecialchars_decode(), html_entity_decode() and get_html_translation_table()
dirname() is a slow function compared with __DIR__ and using
'/../'. Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code. This allows those required includes to perform as
best as possible in this situation.