FIX: N1 issues for bookmark list (#9236)

* Preload custom fields for BookmarkQuery and add preload callback. Copy TopicQuery preload methodology to allow plugins to preload data for the BookmarkQuery. This fixes assigned plugin custom fields N1
* Include topic tags in initial query to avoid tags N1

Related: discourse/discourse-assign#63

lib/bookmark_query.rb

@@ -5,6 +5,19 @@
 # in the user/activity/bookmarks page.
 
 class BookmarkQuery
+  cattr_accessor :preloaded_custom_fields
+  self.preloaded_custom_fields = Set.new
+
+  def self.on_preload(&blk)
+    (@preload ||= Set.new) << blk
+  end
+
+  def self.preload(bookmarks, object)
+    if @preload
+      @preload.each { |preload| preload.call(bookmarks, object) }
+    end
+  end
+
   def initialize(user, params = {})
     @user = user
     @params = params
@@ -15,18 +28,28 @@ class BookmarkQuery
       .joins('INNER JOIN topics ON topics.id = bookmarks.topic_id')
       .joins('INNER JOIN posts ON posts.id = bookmarks.post_id')
       .joins('INNER JOIN users ON users.id = posts.user_id')
-      .order('created_at DESC')
+      .order('bookmarks.created_at DESC')
 
     if @params[:limit]
       results = results.limit(@params[:limit])
     end
 
+    if BookmarkQuery.preloaded_custom_fields.any?
+      Topic.preload_custom_fields(
+        results.map(&:topic), BookmarkQuery.preloaded_custom_fields
+      )
+    end
+
+    BookmarkQuery.preload(results, self)
+
     results
   end
 
   private
 
   def user_bookmarks
-    Bookmark.where(user: @user).includes(:topic).includes(post: :user)
+    Bookmark.where(user: @user)
+      .includes(topic: :tags)
+      .includes(post: :user)
   end
 end