src/Type/Definition/Type.php
public static function isBuiltInType(Type $type)
    {
        return in_array($type->name, array_keys(self::getAllBuiltInTypes()), true);
    }
public static function isBuiltInType(Type $type)
    {
        return in_array($type->name, array_keys(self::getAllBuiltInTypes()), true);
    }
Checks if the type is a builtin type

@return bool