Add docs for DateTimeZoneNormalizer

Author: William Jehanne

components/serializer.rst

@@ -737,6 +737,10 @@ There are several types of normalizers available:
     :phpclass:`DateTime` and :phpclass:`DateTimeImmutable`) into strings.
     By default, it uses the `RFC3339`_ format.
 
+:class:`Symfony\\Component\\Serializer\\Normalizer\\DateTimeZoneNormalizer`
+    This normalizer converts :phpclass:`DateTimeZone` objects into strings.
+    By default, it uses the `RFC3339`_ format.
+
 :class:`Symfony\\Component\\Serializer\\Normalizer\\DataUriNormalizer`
     This normalizer converts :phpclass:`SplFileInfo` objects into a data URI
     string (``data:...``) such that files can be embedded into serialized data.

serializer.rst

@@ -61,6 +61,8 @@ As well as the following normalizers:
   handle typical data objects
 * :class:`Symfony\\Component\\Serializer\\Normalizer\\DateTimeNormalizer` for
   objects implementing the :phpclass:`DateTimeInterface` interface
+* :class:`Symfony\\Component\\Serializer\\Normalizer\\DateTimeZoneNormalizer` for
+  :phpclass:`DateTimeZone` objects
 * :class:`Symfony\\Component\\Serializer\\Normalizer\\DataUriNormalizer` to
   transform :phpclass:`SplFileInfo` objects in `Data URIs`_
 * :class:`Symfony\\Component\\Serializer\\Normalizer\\JsonSerializableNormalizer`