Crashes on config entities that define a canonical link template

Problem/Motivation

A lot of contrib config entities define a canonical link template but not a view builder, e.g. in Entity Share:

 *   links = {
 *     "canonical" = "/admin/config/services/entity_share/channel/{channel}",

This means that this code in Responsive Preview crashes:

      if ($entity->hasLinkTemplate('canonical')) {
        return $entity->toUrl()->toString();
      }

Steps to reproduce

Install a module such as Entity Share and try edit a channel config entity.

Proposed resolution

1. Don't act on config entities
2. Move the check for admin routes to the top of the method, as there's no point doing anything on admin routes

Remaining tasks

User interface changes

API changes

Data model changes