Merge branch '5.4' into 6.0

* 5.4:
  expand uninitialized session tests
  [Lock] Release PostgreSqlStore connection lock on failure
  [DomCrawler] Fix HTML5 parser charset option
  cs fix
  [HttpKernel] Do not attempt to register enum arguments in controller service locator
  [Mime] Fix missing sprintf in DkimSigner
  [Translation] [LocoProvider] Use rawurlencode and separate tag setting
  [Security] fix unserializing session payloads from v4
  [Cache] Don't lock when doing nested computations
  [Messenger] fix Redis support on 32b arch
  [HttpFoundation] Fix notice when HTTP_PHP_AUTH_USER passed without pass
  [Security] Add getting started example to README

Author: nicolas-grekas

README.md

@@ -1,10 +1,16 @@
 Security Component - HTTP Integration
 =====================================
 
-Security provides an infrastructure for sophisticated authorization systems,
-which makes it possible to easily separate the actual authorization logic from
-so called user providers that hold the users credentials. It is inspired by
-the Java Spring framework.
+The Security HTTP component provides an HTTP integration of the Security Core
+component. It allows securing (parts of) your application using firewalls and
+provides authenticators to authenticate visitors.
+
+Getting Started
+---------------
+
+```
+$ composer require symfony/security-http
+```
 
 Sponsor
 -------