Merge branch '2.8' into 3.1

* 2.8:
  [Routing] Fail properly when a route parameter name cannot be used as a PCRE subpattern name
  [FrameworkBundle] Improve performance of ControllerNameParser
  Update documentation link to the component
  [HttpFoundation] Add links to RFC-7231
  [DI] Initialize properties before method calls
  Tag missing internals
  [WebProfilerBundle] Dont use request attributes in RouterController
  Fix complete config tests

Author: nicolas-grekas

Request.php

@@ -1475,6 +1475,8 @@ public function isMethod($method)
     /**
      * Checks whether the method is safe or not.
      *
+     * @see https://tools.ietf.org/html/rfc7231#section-4.2.1
+     *
      * @param bool $andCacheable Adds the additional condition that the method should be cacheable. True by default.
      *
      * @return bool
@@ -1487,6 +1489,8 @@ public function isMethodSafe(/* $andCacheable = true */)
     /**
      * Checks whether the method is cacheable or not.
      *
+     * @see https://tools.ietf.org/html/rfc7231#section-4.2.3
+     *
      * @return bool
      */
     public function isMethodCacheable()