FEATURE: Display unread and new counts for messages. (#14059)

There are certain design decisions that were made in this commit.

Private messages implements its own version of topic tracking state because there are significant differences between regular and private_message topics. Regular topics have to track categories and tags while private messages do not. It is much easier to design the new topic tracking state if we maintain two different classes, instead of trying to mash this two worlds together.

One MessageBus channel per user and one MessageBus channel per group. This allows each user and each group to have their own channel backlog instead of having one global channel which requires the client to filter away unrelated messages.

lib/post_jobs_enqueuer.rb

@@ -20,11 +20,6 @@ class PostJobsEnqueuer
       after_topic_create
       make_visible
     end
-
-    if @topic.private_message?
-      TopicTrackingState.publish_private_message(@topic, post: @post)
-      TopicGroup.new_message_update(@topic.last_poster, @topic.id, @post.post_number)
-    end
   end
 
   private
@@ -46,6 +41,7 @@ class PostJobsEnqueuer
   end
 
   def make_visible
+    return if @topic.private_message?
     return unless SiteSetting.embed_unlisted?
     return unless @post.post_number > 1
     return if @topic.visible?
@@ -73,12 +69,18 @@ class PostJobsEnqueuer
     @topic.posters = @topic.posters_summary
     @topic.posts_count = 1
 
-    TopicTrackingState.publish_new(@topic)
+    klass =
+      if @topic.private_message?
+        PrivateMessageTopicTrackingState
+      else
+        TopicTrackingState
+      end
+
+    klass.publish_new(@topic)
   end
 
   def skip_after_create?
     @opts[:import_mode] ||
-      @topic.private_message? ||
       @post.post_type == Post.types[:moderator_action] ||
       @post.post_type == Post.types[:small_action]
   end