Don't lose values for cmrf_display fields when coming back from preview

Closes #3447564

This also drops the setting of $element['#value'] like !21 (closed) so this fixes #3447541, too.

src/WebformSubmissionHandler.php

@@ -133,6 +133,10 @@ class WebformSubmissionHandler {
         }
       }
     }
+    else {
+      $this->loadDefaultValuesFromStorage($form, $form_state);
+    }
+
     $wrapperId = $form_state->getFormObject()
         ->getFormId() . '_cmrf_form_processor';
     if (!isset($form['#prefix'])) {
@@ -550,6 +554,16 @@ class WebformSubmissionHandler {
     return $params;
   }
 
+  private function loadDefaultValuesFromStorage(array &$form, FormStateInterface $formState): void {
+    $defaults = $formState->get('defaults') ?? [];
+    foreach ($defaults as $field => $value) {
+      $element =& WebformElementHelper::getElement($form, $field);
+      if (NULL !== $element) {
+        $element['#default_value'] ??= $value;
+      }
+    }
+  }
+
   private function setDefaultValue(array &$form, FormStateInterface $formState, WebformSubmissionInterface $webformSubmission, string $field, $value) {
     $element =& WebformElementHelper::getElement($form, $field);
     if ($element) {
@@ -575,27 +589,24 @@ class WebformSubmissionHandler {
             }
             $file->save();
             $element['#default_value'] = [$file->id()];
-            $element['#value'] = $element['#default_value'];
-            $formState->setValue($field, $element['#default_value']);
-            $webformSubmission->setElementData($field, $element['#default_value']);
           }
         }
       } elseif ($element['#type'] == 'datetime') {
         try {
           $value = DrupalDateTime::createFromFormat(\DateTime::ATOM, $value);
           $element['#default_value'] = $value;
-          $element['#value'] = $value;
-          $formState->setValue($field, $value);
-          $webformSubmission->setElementData($field, $value);
         } catch (\InvalidArgumentException $ex) {
           // is it something else than a date ignore
         }
       }
       elseif ($value !== NULL) {
         $element['#default_value'] = $value;
-        $element['#value'] = $value;
-        $formState->setValue($field, $value);
-        $webformSubmission->setElementData($field, $value);
+      }
+
+      if (array_key_exists('#default_value', $element)) {
+        $formState->setValue($field, $element['#default_value']);
+        $formState->set(['defaults', $field], $element['#default_value']);
+        $webformSubmission->setElementData($field, $element['#default_value']);
       }
     }
   }