fix: class_alias with preloading

[sylfabre]

Q	A
Branch?	2.7
Tickets	Closes similar issue to https://github.com/api-platform/core/pull/5523/files
License	MIT
Doc PR	N/A

https://github.com/api-platform/core/blob/2.7/src/Symfony/Validator/EventListener/ValidationExceptionListener.php suffers from the same issue as https://github.com/api-platform/core/pull/5523/files

=> This PR wraps all calls to class_alias() in an if condition to check first if the alias already exists

This is important to us because we want to upgrade first to 2.7 before moving forward to 3.0: we cannot do it right now because preloading breaks with 2.7

This PR follows up on #6217 which was a disaster. This new version has been tested internally within my company and we plan to release it on week 15 (April 8th, 2024)

[sylfabre]

Hello @dpawelec @markom-werbeagentur @ywarnier

Here is a new version that passed tests with preloading and classloading.

Would you please give it a try before asking @soyuka or @dunglas?
Thanks a lot

[sylfabre]

FYI, we have been using our fork in production for about a week without any bug report

[markom-werbeagentur]

Seems to work for me, thank you very much for your work.

[soyuka]

should I merge and tag this then @sylfabre ?

[sylfabre]

Hello @soyuka

So far so good here at AssoConnect.
So I think you can merge safely.

Waiting a bit more for more feedbacks is also a viable option

Up to you!