Entity HTML route patterns standardized

In prior Drupal 8 alpha release the route names for various entities have not been standardized. That meant they were often unpredictable and inconsistent between different entity types and different use cases.

The names for entity-based routes are now standardized around link relationships. A link relationship is a RESTful property of a resource that specifies how one resource relates to another. All entities define some number of link relationships, relying on the IANA standard definitions where possible. All entities need, at minimum, a "canonical" relationship which is the URI at which the entity can be accessed.

The HTML-centric route for any entity/relationship is now entity.$entity_type.$relationship, with all dashes converted to underscores. For example, entity.node.canonical (which corresponds to /node/1), entity.node.edit_form (/node/1/edit) entity.user.canonical (/user/1), etc.

Note: As of this writing the conversion process is still in progress in the linked issues. Also, the intent longer-term is to auto-generate these routes rather than expecting module developers to create them manually. That work is ongoing.