minor #9215 Updated the service naming conventions for modern Symfony apps (javiereguiluz)

This PR was squashed before being merged into the 3.4 branch (closes #9215).

Discussion
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Updated the service naming conventions for modern Symfony apps

This fixes #8390.

Commits
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b7152f7 Updated the service naming conventions for modern Symfony apps

Author: javiereguiluz

contributing/code/standards.rst

@@ -229,15 +229,17 @@ Naming Conventions
 Service Naming Conventions
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-* A service name contains groups, separated by dots;
+* A service name must be the same as the fully qualified class name (FQCN) of
+  its class (e.g. ``App\EventSubscriber\UserSubscriber``);
 
-* The DI alias of the bundle is the first group (e.g. ``fos_user``);
+* If there are multiple services for the same class, use the FQCN for the main
+  service and use lowercased and underscored names for the rest of services.
+  Optionally divide them in groups separated with dots (e.g.
+  ``something.service_name``, ``fos_user.something.service_name``);
 
-* Use lowercase letters for service and parameter names (except when referring
+* Use lowercase letters for parameter names (except when referring
   to environment variables with the ``%env(VARIABLE_NAME)%`` syntax);
 
-* A group name uses the underscore notation;
-
 * Add class aliases for public services (e.g. alias ``Symfony\Component\Something\ClassName``
   to ``something.service_name``).