Confirmation page as entity autocomplete

Patch for the 2.0.2 branch

This looks like it would only work when the destination page is a node, specifically a basic page. This would probably cover most use cases but would cause a problem for the odd site whose destination was another type of entity or custom route.

Updated patch for the 2.2.4 tag
Removed target_bundles so all Content types can be used.

But what about other entity types or custom routes? These are surely rare but I don't want to break existing installations if someone needs to resave the form, and their destination page is no longer allowed by the field.