Issue #3519104: Template not rendered if cloned

Initial commit for: Merge image_sizes_extras into image_sizes; Refactor data model to be built on cores responsive_image module instead of relying on an additional config entity.

Closes #3519104

templates/responsive-image-formatter--image-sizes.html.twig

@@ -19,7 +19,7 @@
 {% apply spaceless %}
   {% set responsive_image %}
     <responsive-img{{ item_attributes }}>
-      <template shadowrootmode="open">
+      <template>
         <img{{ image_attributes }}>
         {% if placeholder_attributes|length %}
           <img{{ placeholder_attributes }}>