Wire the EntityArgumentResolver

[HypeMC]

Resolves #753

Despite "Entity" being in it's name, the EntityValueResolver & #[MapEntity] attribute work with MongoDB documents as well, it's just missing the wiring.
This PR is basically a copy of doctrine/DoctrineBundle#1554 with some minor adjustments.

[malarzm]

@HypeMC don't mind Psalm's failure (unless you want to), we'll deal with that separately

[deluxetom]

Anything I could help with to get this PR merged? this seems ready to me

[franmomu]

Thanks @HypeMC!

[boskos-q]

Thanks @franmomu for merging this!
One more thing, when can we expect for 4.6.x to be released as we'd really need this feature?
Also I don't want to sound like an ignorant dev who just asks for a feature, but if there is anything I could do to help for this release to happen, please do tell. I'll be more than happy to do it :)

[nicolas-grekas]

This should be updated to leverage symfony/symfony#48992! (adding attribute "name" on the tag)

[franmomu]

@boskos-q I'm sorry, but we don't really know, I hope it won't take too much.
You can always try the 4.6.x branch in your project and that would help us to test next release.

There is also #770 that needs to be addressed.