Merge branch '2.8' into 3.4

* 2.8:
  [Form] Fixed keeping hash of equal \DateTimeInterface on submit
  [PhpUnitBridge] Fix typo
  [Config] Unset key during normalization
  invalidate forms on transformation failures

Author: nicolas-grekas

Resources/config/form.xml

@@ -159,6 +159,11 @@
             <deprecated>The "%service_id%" service is deprecated since Symfony 3.1 and will be removed in 4.0.</deprecated>
         </service>
 
+        <service id="form.type_extension.form.transformation_failure_handling" class="Symfony\Component\Form\Extension\Core\Type\TransformationFailureExtension">
+            <tag name="form.type_extension" extended-type="Symfony\Component\Form\Extension\Core\Type\FormType" />
+            <argument type="service" id="translator" on-invalid="ignore" />
+        </service>
+
         <!-- FormTypeHttpFoundationExtension -->
         <service id="form.type_extension.form.http_foundation" class="Symfony\Component\Form\Extension\HttpFoundation\Type\FormTypeHttpFoundationExtension">
             <argument type="service" id="form.type_extension.form.request_handler" />