PHP 8 compatibility

[alan-ps]

There is fatal error happen when we try to use the module with php8.

PHP Fatal error: Declaration of Doctrine\\Common\\Reflection\\StaticReflectionClass::getConstants() must be compatible with ReflectionClass::getConstants(?int $filter = null) in plug/lib/doctrine/common/lib/Doctrine/Common/Reflection/StaticReflectionClass.php on line 109

I would suggest to apply a patch from doctrine/reflection#49, which actually fixes compatibility issue for doctrine/reflection.

[alan-ps]

Create a PR based on ticket description: #49