[Config][DependencyInjection][Routing] Deprecate using `$this` or the i…

[nicolas-grekas]

Q	A
Feature PR	symfony/symfony#61860
PR author(s)	@nicolas-grekas
Merged in	7.4

We created this issue to not forget to document this new feature. We would really appreciate if you can help us with this task. If you are not sure how to do it, please ask us and we will help you.

To fix this issue, please create a PR against the 7.4 branch in the symfony-docs repository.

Thank you! :smiley:

[stof]

I found some usages in https://symfony.com/doc/current/service_container.html#multiple-service-definitions-using-the-same-namespace

the PHP snippet should probably be updated to use the PHP DSL (also used in the previous snippet) instead of the lower-level loader API.