Data-align value unavailable in filters for CKEditor 5 previews

Here's the most straight-forward solution I could come up with (patch attached).

This patch: Passes a boolean to the CKEditor 5 plugin of whether the Drupal core alignment filter is enabled. If it's disabled (i.e. we can safely assume that the `data-align` attribute is unused unless the site has a custom filter enabled), then we don't add data-align to the attribute ignore list so that any custom filters can handle it.

Another option would be to simply rename the attribute to `data-removed-align` or something rather than removing it completely, but that would require the filter to check both attributes and seems more convoluted overall.

Any input appreciated, thanks.

I've run into this as well, but note that I do use core's FilterAlign text filter. But what I do is alter the embed like this:

function HOOK_entity_embed_alter(array &$build, EntityInterface $entity, array &$context) {
  // Pass the data-align attribute down to the entity render data, because
  // we want the alignment classes added to the HTML for the entity and not
  // the "container" div that entity embed wraps it in. In fact, we remove that
  // container div entirely via a template override in ps_base theme because
  // we don't want the extra markup.
  // No need to mess with cache key, since embedded entities are already not
  // cached.
  // Note that since the FilterAlign filter runs before this code, it has
  // already set the alignment class, so we need to check for it there instead
  // of from the data attribute.
  foreach (['align-left', 'align-center', 'align-right'] as $alignmentClass) {
    if (isset($context['class']) && in_array($alignmentClass, $context['class'])) {
      $build['entity']['#attributes']['class'][] = $alignmentClass;
    }
  }
}

So I run into the same problem, in that when the embed is being previewed within the editor, this code doesn't actually have any alignment class to work with as the CKE plugin removed it for the preview. Things do work fine otherwise though.

I think for now, I'm just going to try and hack around this with my ckeditor5-stylesheet, but not ideal.