Deprecate node_is_page and move into a service

Is there not an existing interface we can add this one vs adding a new one. Think it should be documented why that is necessary

📌 Deprecate $variables['page'] for node.html.twig Active is trying to deprecate this with no replacement. I think we should try to get that done first, so postponing on that issue.

Closing this as a duplicate of 📌 Deprecate $variables['page'] for node.html.twig Active