DEV: use structured data in crawler-linkback-list for referencing only (#16237)

This simplifies the crawler-linkback-list to only be a point of reference to the actual DiscussionForumPosting objects.

See "Summary page": https://developers.google.com/search/docs/advanced/structured-data/carousel?hl=en#summary-page
> [It] defines an ItemList, where each ListItem has only three properties: @type (set to ListItem), position (the position in the list), and url (the URL of a page with full details about that item).

app/views/topics/show.html.erb

@@ -103,10 +103,7 @@
               <% @topic_view.link_counts[post.id].each_with_index do |link, i| %>
                 <% if link[:reflection] && link[:title].present? %>
                   <div itemprop='itemListElement' itemscope itemtype='http://schema.org/ListItem'>
-                    <a href="<%=link[:url]%>" itemscope itemtype='http://schema.org/DiscussionForumPosting' itemprop='item'>
+                    <a itemprop='url' href="<%=link[:url]%>"><%=link[:title]%></a>
-                      <meta itemprop='url' content='<%=link[:url]%>'>
-                      <span itemprop='name'><%=link[:title]%></span>
-                    </a>
                     <meta itemprop='position' content='<%= i+1 %>'>
                   </div>
                 <% end %>

spec/views/topics/show.html.erb_spec.rb

@@ -18,4 +18,27 @@ RSpec.describe "topics/show.html.erb" do
       %r{<link rel="alternate nofollow" type="application/rss\+xml" title="[^"]+" href="https://www.example.com/test\.rss" />},
     )
   end
+
+  it "adds sturctured data" do
+    view.stubs(:include_crawler_content?).returns(true)
+    post = Fabricate(:post, topic: topic)
+    TopicLink.create!(
+      topic_id: post.topic_id,
+      post_id: post.id,
+      user_id: post.user_id,
+      url: "https://example.com/",
+      domain: "example.com",
+      link_topic_id: Fabricate(:topic).id,
+      reflection: true,
+    )
+    assign(:topic_view, TopicView.new(topic))
+    assign(:tags, [])
+
+    render template: "topics/show", formats: [:html]
+
+    links_list = Nokogiri::HTML5.fragment(rendered).css(".crawler-linkback-list")
+    first_item = links_list.css('[itemprop="itemListElement"]')
+    expect(first_item.css('[itemprop="position"]')[0]["content"]).to eq("1")
+    expect(first_item.css('[itemprop="url"]')[0]["href"]).to eq("https://example.com/")
+  end
 end