Update DrupalBlockProcessor.php to add classes as attributes

Instead of having a wrapping div for the CSS classname to be added to this change passes both the custom class name and the align class name into the attributes class array for rendering in the block template.

Closes #3260340

src/BlockProcessor/DrupalBlockProcessor.php

@@ -87,10 +87,15 @@ class DrupalBlockProcessor implements GutenbergBlockProcessorInterface {
       $render = [
         'content' => $render_content,
       ];
-      // Render the css class if available.
+
+      // Add the CSS class if available.
       if (!empty($block_attributes['className'])) {
-        $render['#prefix'] = sprintf('<div class="%s">', Html::escape($block_attributes['className']));
-        $render['#suffix'] = '</div>';
+        $render['content']['#attributes']['class'][] = Html::escape($block_attributes['className']);
+      }
+
+      // Add the align CSS class if available.
+      if (!empty($block_attributes['align'])) {
+        $render['content']['#attributes']['class'][] = 'align' . $block_attributes['align'];
       }
 
       $block_content = $this->renderer->render($render);