minor #10313 Update 3.3-di-changes.rst (DonCallisto)

This PR was submitted for the master branch but it was squashed and merged into the 3.4 branch instead (closes #10313).

Discussion
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Update 3.3-di-changes.rst

Looking at deprecations of 4.2, I noticed that extending `AbstractController` will prevent you from getting the services (even public ones) from container. This should be reported.

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Commits
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f16e631 Update 3.3-di-changes.rst

Author: javiereguiluz

service_container/3.3-di-changes.rst

@@ -585,6 +585,13 @@ Start by updating the service ids to class names:
     account when looking up for services.
     Furthermore it is always recommended to check for definition existence
     using ``has()`` function.
+    
+.. note::
+
+    If you get rid of deprecations and extend ``AbstractController`` instead of ``Controller`` for
+    your controllers, you can skip the rest of this step as `AbstractController` won't provide a 
+    container where you can get the services directly. All services need to be injected as explained 
+    in the :ref:`step 5 of this article <step-5>`.
 
 But, this change will break our app! The old service ids (e.g. ``app.github_notifier``)
 no longer exist. The simplest way to fix this is to find all your old service ids
@@ -716,6 +723,8 @@ will be used. If you *don't* have this, the auto-registration feature will try t
 register a third ``ApiClient`` service and use that for autowiring (which will fail,
 because the class has a non-autowireable argument).
 
+.. _step-5:
+
 Step 5) Cleanup!
 ~~~~~~~~~~~~~~~~