feature symfony#18483 [Serializer] Deprecate SerializerAwareEncoder (JhonnyL)

This PR was merged into the 3.2-dev branch.

Discussion
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[Serializer] Deprecate SerializerAwareEncoder

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
-------

af57467 [Serializer] Deprecate SerializerAwareEncoder

Author: fabpot

src/Symfony/Component/Serializer/Encoder/SerializerAwareEncoder.php

@@ -11,23 +11,17 @@
 
 namespace Symfony\Component\Serializer\Encoder;
 
-use Symfony\Component\Serializer\SerializerInterface;
 use Symfony\Component\Serializer\SerializerAwareInterface;
+use Symfony\Component\Serializer\SerializerAwareTrait;
 
 /**
  * SerializerAware Encoder implementation.
  *
  * @author Jordi Boggiano <[email protected]>
+ *
+ * @deprecated since version 3.2, to be removed in 4.0. Use the SerializerAwareTrait instead.
  */
 abstract class SerializerAwareEncoder implements SerializerAwareInterface
 {
-    protected $serializer;
-
-    /**
-     * {@inheritdoc}
-     */
-    public function setSerializer(SerializerInterface $serializer)
-    {
-        $this->serializer = $serializer;
-    }
+    use SerializerAwareTrait;
 }