Use the new entity: URI scheme

Problem/Motivation

https://www.drupal.org/node/2406749#comment-9569221 - this patch left to use node path but we would like to use entity:uri.

Follow-up to #2406749-56: Use a link field for custom menu link

// Create a new menu_link_content entity.
        $entity = entity_create('menu_link_content', array(
          'title' => trim($definition['title']),
          'description' => trim($definition['description']),
          // @todo Replace it with entity: once possible.
          'link' => ['uri' => 'node/' . $node->id()],
          'menu_name' => $definition['menu_name'],
          'parent' => $definition['parent'],
          'weight' => isset($definition['weight']) ? $definition['weight'] : 0,
          'enabled' => 1,
          'langcode' => $node->getUntranslated()->language()->getId(),
        ));

#2411333: Create standard logic to handle a entity: URI scheme is in
so use it.

The tests around this could be tricky.

Proposed resolution

Use entity:

Remaining tasks

User interface changes

No

API changes

No