Normalize fragment before appending

Closes #3479770

src/Plugin/Filter/EmbeddedContent.php

@@ -101,7 +101,8 @@ class EmbeddedContent extends FilterBase implements ContainerFactoryPluginInterf
           ))->render();
       }
       $fragment = $document->createDocumentFragment();
-      $fragment->appendXML($render);
+      $html = Html::normalize($render);
+      $fragment->appendXML($html);
       $node->parentNode->replaceChild($fragment, $node);
     }
     $result = new FilterProcessResult(Html::serialize($document));