Merge branch '5.0' into 5.1

* 5.0:
  Fix abstract method name in PHP doc block
  Various cleanups
  [HttpClient] fix issues in tests
  Fixes sprintf(): Too few arguments in form transformer
  [Console] Fix QuestionHelper::disableStty()
  [Validator] Use Mime component to determine mime type for file validator
  validate subforms in all validation groups
  Update Hungarian translations
  Add meaningful message when Process is not installed (ProcessHelper)
  [PropertyAccess] Fix TypeError parsing again.
  [TwigBridge] fix fallback html-to-txt body converter
  [Security/Http] fix merge
  [ErrorHandler] fix setting $trace to null in FatalError
  [Form] add missing Czech validators translation
  [Validator] add missing Czech translations
  never directly validate Existence (Required/Optional) constraints

Author: nicolas-grekas

Process.php

@@ -1608,7 +1608,7 @@ private function replacePlaceholders(string $commandline, array $env)
     {
         return preg_replace_callback('/"\$\{:([_a-zA-Z]++[_a-zA-Z0-9]*+)\}"/', function ($matches) use ($commandline, $env) {
             if (!isset($env[$matches[1]]) || false === $env[$matches[1]]) {
-                throw new InvalidArgumentException(sprintf('Command line is missing a value for parameter "%s": '.$commandline, $matches[1]));
+                throw new InvalidArgumentException(sprintf('Command line is missing a value for parameter "%s": ', $matches[1]).$commandline);
             }
 
             return $this->escapeArgument($env[$matches[1]]);