posts: refactor post previews to use ViewComponent.

Refactor the post preview html to use the ViewComponent framework. This
lets us encapsulate all the HTML, CSS, and helper methods for a UI
component in a single place.

See https://viewcomponent.org.

app/components/post_preview_component/post_preview_component.html.erb

@@ -0,0 +1,47 @@
+<%= tag.article id: "post_#{post.id}", **article_attrs do -%>
+  <%= link_to polymorphic_path(link_target, link_params) do -%>
+    <picture>
+      <%= tag.source media: "(max-width: 660px)", srcset: cropped_url -%>
+      <%= tag.source media: "(min-width: 660px)", srcset: post.preview_file_url -%>
+      <%= tag.img class: "has-cropped-#{post.has_cropped?}", src: post.preview_file_url, style: "min-width: #{preview_dimensions[:width]}px; min-height: #{preview_dimensions[:height]}px;", title: tooltip, alt: "post ##{post.id}" -%>
+    </picture>
+  <% end -%>
+  <% if pool -%>
+    <p class="desc">
+      <%= link_to pool.pretty_name.truncate(80), pool %>
+    </p>
+  <% end -%>
+  <% if similarity -%>
+    <p class="desc">
+      <% if post.source =~ %r!\Ahttps?://!i %>
+        <%= external_link_to post.normalized_source, post.source_domain %>
+        (<%= time_ago_in_words_tagged(post.created_at, compact: true) %>)
+      <% else %>
+        <%= time_ago_in_words_tagged(post.created_at, compact: true) %>
+      <% end %>
+    </p>
+  <% end %>
+  <% if size -%>
+    <p class="desc">
+      <%= link_to number_to_human_size(size), post.file_url %>
+      (<%= post.image_width %>x<%= post.image_height %>)
+    </p>
+  <% end -%>
+  <% if similarity -%>
+    <p class="desc">
+      <%= link_to "#{similarity}%", iqdb_queries_path(post_id: post.id) %> similarity
+    </p>
+  <% end -%>
+
+  <% if recommended -%>
+    <p class="desc recommended">
+      <%= link_to recommended_posts_path(search: { post_id: post.id }), class: "more-recommended-posts", "data-post-id": post.id do %>
+        <%= post.fav_count %>
+
+        <i class="far fa-heart fa-xs"></i>
+
+        <br>more »
+      <% end %>
+    </p>
+  <% end -%>
+<% end -%>