Merge branch '5.0' into 5.1

* 5.0:
  [DependencyInjection][CheckTypeDeclarationsPass] Handle unresolved parameters pointing to environment variables
  switch the context when validating nested forms
  remove unused param from validator service config
  Fix typo
  [HttpKernel] Fix regression where Store does not return response body correctly
  rework form validator tests
  Update AbstractController.php

Controller/AbstractController.php

@@ -197,7 +197,7 @@ protected function file($file, string $fileName = null, string $disposition = Re
      *
      * @throws \LogicException
      */
-    protected function addFlash(string $type, string $message): void
+    protected function addFlash(string $type, $message): void
     {
         if (!$this->container->has('session')) {
             throw new \LogicException('You can not use the addFlash method if sessions are disabled. Enable them in "config/packages/framework.yaml".');

Resources/config/validator.xml

@@ -5,7 +5,6 @@
     xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd">
 
     <parameters>
-        <parameter key="validator.mapping.cache.prefix" />
         <parameter key="validator.mapping.cache.file">%kernel.cache_dir%/validation.php</parameter>
     </parameters>