Support additional top-level data in returns from ApiPreviewController

This would also help https://git.drupalcode.org/project/experience_builder/-/merge_requests/496

Two nits but otherwise this looks good to me and unblocks at least three other issues.

Merging to unblock ✨ Show page information in top bar Active .

Automatically closed - issue fixed for 2 weeks with no activity.

wim leers → made their first commit to this issue’s fork.

🤩 final class PreviewEnvelope

AFAICT XBPreviewRenderer now is no longer a main content renderer (a MainContentRendererInterface implementation that is a render.main_content_renderer-tagged service), nor does it need to be a (private) service, because nothing uses ?_wrapper_format=xb_preview anymore? 🤔

I wanted to merge the logic in \Drupal\experience_builder\Render\MainContent\XBPreviewRenderer into \Drupal\experience_builder\EventSubscriber\PreviewEnvelopeViewSubscriber, but turns out that's not easily possible because we want to maximally reuse \Drupal\Core\Render\MainContent\HtmlRenderer logic.

So, proposed an MR to clarify that.

Thanks! 🤝

Automatically closed - issue fixed for 2 weeks with no activity.