Merge branch '2.7' into 2.8

* 2.7: (40 commits)
  [Debug] Fix ClassNotFoundFatalErrorHandler candidates lookups
  [2.6][Translator] Extend, refactor and simplify Translator tests.
  Update DebugClassLoader.php
  inject asset packages in assets helper service
  [travis] Do not exclude legacy tests on 2.7
  [HttpFoundation] remove getExtension method
  [2.6][Translation] fix legacy tests.
  [Form] Removed remaining deprecation notices in the test suite
  [Form] Moved deprecation notice triggers to file level
  [Debug] Map PHP errors to LogLevel::CRITICAL
  [Routing][DependencyInjection] Support .yaml extension in YAML loaders
  [DX] improve file loader error for router/other resources in bundle
  [FrameworkBundle] Initialize translator with the default locale.
  [FrameworkBundle] Fix Routing\DelegatingLoader resiliency to fatal errors
  [2.7][Translation] remove duplicate code for loading catalogue.
  [2.6][Translation] remove duplicate code for loading catalogue.
  [HttpKernel] Cleanup ExceptionListener
  CS fixes
  [DependencyInjection] Show better error when the Yaml component is not installed
  [2.3] SCA for Components - reference mismatches
  ...

Author: nicolas-grekas

composer.json

@@ -34,9 +34,8 @@
         "symfony/property-access": "For using the ObjectNormalizer."
     },
     "autoload": {
-        "psr-0": { "Symfony\\Component\\Serializer\\": "" }
+        "psr-4": { "Symfony\\Component\\Serializer\\": "" }
     },
-    "target-dir": "Symfony/Component/Serializer",
     "minimum-stability": "dev",
     "extra": {
         "branch-alias": {