FIX: Remove tags from experimental sidebar on notification level changed (#17083)

As part of this commit, a bug where updating a tag's notification level on the server side does not update the state of the user's tag notification levels on the client side is fixed too.

app/serializers/current_user_serializer.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 class CurrentUserSerializer < BasicUserSerializer
+  include UserTagNotificationsMixin
 
   attributes :name,
              :unread_notifications,
@@ -33,7 +34,6 @@ class CurrentUserSerializer < BasicUserSerializer
              :tracked_category_ids,
              :watched_first_post_category_ids,
              :watched_category_ids,
-             :muted_tag_ids,
              :watched_tags,
              :watching_first_post_tags,
              :tracked_tags,
@@ -230,32 +230,6 @@ class CurrentUserSerializer < BasicUserSerializer
     categories_with_notification_level(:watching_first_post)
   end
 
-  # this is a weird outlier that is used for topic tracking state which
-  # needs the actual ids, which is why it is duplicated with muted_tags
-  def muted_tag_ids
-    TagUser.lookup(object, :muted).pluck(:tag_id)
-  end
-
-  def muted_tags
-    tags_with_notification_level(:muted)
-  end
-
-  def tracked_tags
-    tags_with_notification_level(:tracking)
-  end
-
-  def watching_first_post_tags
-    tags_with_notification_level(:watching_first_post)
-  end
-
-  def watched_tags
-    tags_with_notification_level(:watching)
-  end
-
-  def regular_tags
-    tags_with_notification_level(:regular)
-  end
-
   def ignored_users
     IgnoredUser.where(user: object.id).joins(:ignored_user).pluck(:username)
   end