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/views/posts/update.js.erb

@@ -1,6 +1,6 @@
 <% if @post.valid? %>
   var $post = $("#post_<%= @post.id %>");
-  var $new_post = $("<%= j PostPresenter.preview(@post, show_deleted: true) %>");
+  var $new_post = $("<%= j post_preview(@post, show_deleted: true) %>");
   Danbooru.Blacklist.apply_post($new_post.get(0));
   $("#post_<%= @post.id %>").replaceWith($new_post);
   <% if params[:mode] == "quick-edit" %>