feature symfony#25839 [SecurityBundle] Deprecate in_memory.user abstract service (chalasr)

This PR was merged into the 4.1-dev branch.

Discussion
----------

[SecurityBundle] Deprecate in_memory.user abstract service

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | symfony#25837 (comment)
| License       | MIT
| Doc PR        | n/a

Commits
-------

75a4117 [SecurityBundle] Deprecate in_memory.user abstract service

Author: fabpot

src/Symfony/Bundle/SecurityBundle/Resources/config/security.xml

@@ -164,7 +164,9 @@
 
         <!-- Provisioning -->
         <service id="security.user.provider.in_memory" class="Symfony\Component\Security\Core\User\InMemoryUserProvider" abstract="true" />
-        <service id="security.user.provider.in_memory.user" class="Symfony\Component\Security\Core\User\User" abstract="true" />
+        <service id="security.user.provider.in_memory.user" class="Symfony\Component\Security\Core\User\User" abstract="true">
+            <deprecated>The "%service_id%" service is deprecated since Symfony 4.1 and will be removed in 5.0.</deprecated>
+        </service>
 
         <service id="security.user.provider.ldap" class="Symfony\Component\Security\Core\User\LdapUserProvider" abstract="true">
             <argument /> <!-- security.ldap.ldap -->