Merge branch '3.4' into 4.1

* 3.4:
  [Debug] ignore underscore vs backslash namespaces in DebugClassLoader
  [TwigBridge][Form] Prevent multiple rendering of form collection prototypes
  [FrameworkBundle] fix describing routes with no controllers
  [DI] move RegisterServiceSubscribersPass before DecoratorServicePass
  Update ValidationListener.php
  [Yaml] ensures that the mb_internal_encoding is reset to its initial value
  [WebLink] Fixed documentation link
  [Security] getTargetPath of TargetPathTrait must return string or null
  [Hackday][Serializer] Deserialization ignores argument type hint from phpdoc for array in constructor argument
  [Security] defer log message in guard authenticator
  merge conflicts
  Fix HeaderBag::get phpdoc

Author: nicolas-grekas

README.md

@@ -11,7 +11,7 @@ It can also be used with extensions defined in the [HTML5 link type extensions w
 Resources
 ---------
 
-  * [Documentation](https://symfony.com/doc/current/components/weblink/introduction.html)
+  * [Documentation](https://symfony.com/doc/current/components/web_link.html)
   * [Contributing](https://symfony.com/doc/current/contributing/index.html)
   * [Report issues](https://github.com/symfony/symfony/issues) and
     [send Pull Requests](https://github.com/symfony/symfony/pulls)