Merge branch '4.3' into 4.4

* 4.3:
  [Serializer] Fix DataUriNormalizer deprecation (MIME type guesser is optional)
  [DependencyInjection] fix the ValidateEnvPlaceHolderPassTest that was using a deprecated path for TreeBuilder
  avoid service id conflicts with Swiftmailer
  [Form] fix usage of legacy TranslatorInterface
  [Serializer] Fix DataUriNormalizer docblock & composer suggest section

Author: nicolas-grekas

composer.json

@@ -34,7 +34,7 @@
         "symfony/cache": "^3.4|^4.0|^5.0",
         "symfony/property-access": "^3.4|^4.0|^5.0",
         "symfony/property-info": "^3.4|^4.0|^5.0",
-        "symfony/translation": "^5.0",
+        "symfony/translation": "^4.4",
         "doctrine/annotations": "~1.0",
         "doctrine/cache": "~1.0",
         "egulias/email-validator": "^1.2.8|~2.0"