Add support for zircore/swagger-php 4.0

[alshenetsky]

Which is introducing php 8.1 attributes support

[GuilhemN]

Thanks for submitting this PR!

It looks like they introduced some more changes, notably @OA\Undefined was moved to Generator::UNDEFINED (see https://github.com/zircote/swagger-php/blob/master/src/Generator.php#L50), and a migration guide is available at https://github.com/zircote/swagger-php/blob/master/docs/Migrating-to-v4.md.

[alshenetsky]

@GuilhemN I'm sorry for being flippant at first. Fixed, and all the tests are passing with v4. But the code is backwards incompatible with the v3 version of zircotte/swagger-php. Do I still have to fix it to get it back compatible with v3? Or will nelmio/api-doc-bundle also have a major version? Sorry for probably stupid question, I just haven't yet come up with an elegant solution to support both versions.

[GuilhemN]

No worry, it is very nice of you to start this pull request, I appreciate it very much :)

I believe bumping our requirement on zircote/swagger-php to 3.2.0 should be enough, isn't it? (changes in the API were normally done in this version, see zircote/swagger-php@c5f0819)

[alshenetsky]

@GuilhemN you are right. But I also had to add compatibility layer with 3.2 because of $context property which was moved to another class in 4.0. You can review it now :)

[GuilhemN]

Thank you! It's a very promising change :)