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

Normalizer/DateTimeNormalizer.php

@@ -94,7 +94,7 @@ public function denormalize($data, string $type, string $format = null, array $c
 
             $dateTimeErrors = \DateTime::class === $type ? \DateTime::getLastErrors() : \DateTimeImmutable::getLastErrors();
 
-            throw new NotNormalizableValueException(sprintf('Parsing datetime string "%s" using format "%s" resulted in %d errors:.'."\n".'%s', $data, $dateTimeFormat, $dateTimeErrors['error_count'], implode("\n", $this->formatDateTimeErrors($dateTimeErrors['errors']))));
+            throw new NotNormalizableValueException(sprintf('Parsing datetime string "%s" using format "%s" resulted in %d errors: ', $data, $dateTimeFormat, $dateTimeErrors['error_count'])."\n".implode("\n", $this->formatDateTimeErrors($dateTimeErrors['errors'])));
         }
 
         try {