Merge branch '2.8' into 3.4

* 2.8:
  [appveyor] fix
  Revert "minor #28321 [Routing] Fixed the interface description of the url generator interface (Toflar)"
  remove cache warmers when Twig cache is disabled
  [HttpKernel][FrameworkBundle] Fix escaping of serialized payloads passed to test clients
  chore: rename Appveyor filename
  Fixed the interface description of the url generator interface
  Format file size in validation message according to binaryFormat option

Author: nicolas-grekas

Client.php

@@ -161,8 +161,8 @@ protected function doRequestInProcess($request)
      */
     protected function getScript($request)
     {
-        $kernel = str_replace("'", "\\'", serialize($this->kernel));
-        $request = str_replace("'", "\\'", serialize($request));
+        $kernel = var_export(serialize($this->kernel), true);
+        $request = var_export(serialize($request), true);
         $errorReporting = error_reporting();
 
         $requires = '';
@@ -171,7 +171,7 @@ protected function getScript($request)
                 $r = new \ReflectionClass($class);
                 $file = \dirname(\dirname($r->getFileName())).'/autoload.php';
                 if (file_exists($file)) {
-                    $requires .= "require_once '".str_replace("'", "\\'", $file)."';\n";
+                    $requires .= 'require_once '.var_export($file, true).";\n";
                 }
             }
         }
@@ -180,7 +180,7 @@ protected function getScript($request)
             throw new \RuntimeException('Composer autoloader not found.');
         }
 
-        $requires .= "require_once '".str_replace("'", "\\'", (new \ReflectionObject($this->kernel))->getFileName())."';\n";
+        $requires .= 'require_once '.var_export((new \ReflectionObject($this->kernel))->getFileName(), true).";\n";
 
         $profilerCode = '';
         if ($this->profiler) {
@@ -194,11 +194,11 @@ protected function getScript($request)
 
 $requires
 
-\$kernel = unserialize('$kernel');
+\$kernel = unserialize($kernel);
 \$kernel->boot();
 $profilerCode
 
-\$request = unserialize('$request');
+\$request = unserialize($request);
 EOF;
 
         return $code.$this->getHandleScript();