Soclass_exists is no longer needed in favor ofcontainer.preload tag do add classes to*.preload.php dumped file ?

@michaljusiega AFAIU, the class_exists were solving 2 issues:

• discovery of classes to be preloaded
• compatibility with preloading is some specific cases related to anonymous classes which break if the class is not loaded

This PR provides an alternative solution to the first issue (thoughclass_exists will still work). For the second problem,class_exists is still the proper solution IMO, as that's not about the Symfony preload dumper by itself, but about compat with preloading.

I updated the PR to now also provide acontainer.no_preload tag.
I added it to eg. console commands.

@michaljusiega: what@stof said:class_exists() are better options for portability and for locality.container.preload serves adding preloading info to third party packages that don't (want to) useclass_exists(), and also in programmatic situations where a bundle's logic might known better about fine grained preloading, depending on the configuration.

@nicolas-grekas,@stof I understand. Thanks!

Thank you@nicolas-grekas.