Auto references are not listed on entity_mesh tables

Problem/Motivation

Creating the PHPUnit test we saw that the auto reference links are not listed, maybe we should create a subcategory called auto-reference or similar, and include on the table.

Steps to reproduce

Example extracted from PHPUnit test:

    // Create HTML content containing various link scenarios.
    $html = '
      <p>External link: <a href="https://example.com">Example</a></p>
      <p>Internal valid link: <a href="/node/1">Internal Node</a></p>
      <p>Broken link: <a href="/non-existent">Broken</a></p>
      <p>Iframe content: <iframe src="https://example.com/iframe"></iframe></p>
    ';

    // Create a node entity in English.
    $node_en = Node::create([
      'type' => 'page',
      'title' => 'Test Node EN',
      'nid' => 1,
      'body' => [
        'value' => $html,
        'format' => 'basic_html',
      ],
      'langcode' => 'en',
    ]);
    $node_en->save();

    // Create a node entity in French.
    $node_fr = Node::create([
      'type' => 'page',
      'title' => 'Test Node FR',
      'nid' => 2,
      'body' => [
        'value' => $html,
        'format' => 'basic_html',
      ],
      'langcode' => 'fr',
    ]);
    $node_fr->save();

    $connection = $this->container->get('database');
    $query = $connection->select('entity_mesh', 'em')
      ->fields('em', [
        'id',
        'type',
        'category',
        'subcategory',
        'source_entity_type',
        'source_entity_bundle',
        'source_entity_id',
        'source_entity_langcode',
        'source_title',
        'target_href',
        'target_path',
        'target_link_type',
        'target_entity_type',
        'target_entity_bundle',
        'target_entity_id',
        'target_entity_langcode',
        'target_title',
      ]);
    $results = $query->execute()->fetchAllAssoc('id', \PDO::FETCH_ASSOC);

Links:

Array
(
    [1] => Array
        (
            [id] => 1
            [type] => entity_render
            [category] => link
            [subcategory] => link
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 1
            [source_entity_langcode] => en
            [source_title] => Test Node EN (node - 1)
            [target_href] => https://example.com
            [target_path] => 
            [target_link_type] => external
            [target_entity_type] => 
            [target_entity_bundle] => 
            [target_entity_id] => 
            [target_entity_langcode] => 
            [target_title] => https://example.com (external)
        )

    [2] => Array
        (
            [id] => 2
            [type] => entity_render
            [category] => link
            [subcategory] => broken-link
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 1
            [source_entity_langcode] => en
            [source_title] => Test Node EN (node - 1)
            [target_href] => /non-existent
            [target_path] => /non-existent
            [target_link_type] => internal
            [target_entity_type] => 
            [target_entity_bundle] => 
            [target_entity_id] => 
            [target_entity_langcode] => 
            [target_title] => /non-existent ()
        )

    [3] => Array
        (
            [id] => 3
            [type] => entity_render
            [category] => iframe
            [subcategory] => iframe
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 1
            [source_entity_langcode] => en
            [source_title] => Test Node EN (node - 1)
            [target_href] => https://example.com/iframe
            [target_path] => 
            [target_link_type] => external
            [target_entity_type] => 
            [target_entity_bundle] => 
            [target_entity_id] => 
            [target_entity_langcode] => 
            [target_title] => https://example.com/iframe (external)
        )

    [4] => Array
        (
            [id] => 4
            [type] => entity_render
            [category] => link
            [subcategory] => link
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 2
            [source_entity_langcode] => fr
            [source_title] => Test Node FR (node - 2)
            [target_href] => https://example.com
            [target_path] => 
            [target_link_type] => external
            [target_entity_type] => 
            [target_entity_bundle] => 
            [target_entity_id] => 
            [target_entity_langcode] => 
            [target_title] => https://example.com (external)
        )

    [5] => Array
        (
            [id] => 5
            [type] => entity_render
            [category] => link
            [subcategory] => link
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 2
            [source_entity_langcode] => fr
            [source_title] => Test Node FR (node - 2)
            [target_href] => /node/1
            [target_path] => /node/1
            [target_link_type] => internal
            [target_entity_type] => node
            [target_entity_bundle] => page
            [target_entity_id] => 1
            [target_entity_langcode] => 
            [target_title] => Test Node EN (node - 1)
        )

    [6] => Array
        (
            [id] => 6
            [type] => entity_render
            [category] => link
            [subcategory] => broken-link
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 2
            [source_entity_langcode] => fr
            [source_title] => Test Node FR (node - 2)
            [target_href] => /non-existent
            [target_path] => /non-existent
            [target_link_type] => internal
            [target_entity_type] => 
            [target_entity_bundle] => 
            [target_entity_id] => 
            [target_entity_langcode] => 
            [target_title] => /non-existent ()
        )

    [7] => Array
        (
            [id] => 7
            [type] => entity_render
            [category] => iframe
            [subcategory] => iframe
            [source_entity_type] => node
            [source_entity_bundle] => page
            [source_entity_id] => 2
            [source_entity_langcode] => fr
            [source_title] => Test Node FR (node - 2)
            [target_href] => https://example.com/iframe
            [target_path] => 
            [target_link_type] => external
            [target_entity_type] => 
            [target_entity_bundle] => 
            [target_entity_id] => 
            [target_entity_langcode] => 
            [target_title] => https://example.com/iframe (external)
        )

)