Merge branch '5.1'

* 5.1:
  [FrameworkBundle] adopt src/.preload.php
  [Cache] Fix key encoding issue in Memcached adapter
  [HttpClient] Fix Array to string conversion notice when parsing JSON error body with non-scalar detail property

Author: fabpot

Command/CacheClearCommand.php

@@ -199,7 +199,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
         $preloadFile = $fs->makePathRelative(\dirname($containerFile, 2), $kernelDir);
         $preloadFile .= substr_replace(basename($containerFile), '.preload', -4, 0);
         $preloadFile = var_export('/'.$preloadFile, true);
-        @file_put_contents($kernelDir.'/preload.php', <<<EOPHP
+        @file_put_contents($kernelDir.'/.preload.php', <<<EOPHP
 <?php
 
 if (file_exists(__DIR__.$preloadFile)) {