PERF: Improve query performance all inbox private messages. (#14304)

First reported in https://meta.discourse.org/t/-/202482/19

There are two optimizations being applied here:

1. Fetch a user's group ids in a seperate query instead of including it
   as a sub-query. When I tried a subquery, the query plan becomes very
inefficient.

1. Join against the `topic_allowed_users` and `topic_allowed_groups`
   table instead of doing an IN against a subquery where we UNION the
`topic_id`s from the two tables. From my profiling, this enables PG to
do a backwards index scan on the `index_topics_on_timestamps_private`
index.

This commit fixes a bug where listing all messages was incorrectly
excluding topics if a topic has been archived by a group even if the
user did not belong to the group.

This commit also fixes another bug where dismissing private messages
selectively was subjected to the default limit of 30.

app/controllers/topics_controller.rb

@@ -952,7 +952,7 @@ class TopicsController < ApplicationController
   end
 
   def private_message_reset_new
-    topic_query = TopicQuery.new(current_user)
+    topic_query = TopicQuery.new(current_user, limit: false)
 
     if params[:topic_ids].present?
       unless Array === params[:topic_ids]
@@ -968,13 +968,12 @@ class TopicsController < ApplicationController
       params.require(:inbox)
       inbox = params[:inbox].to_s
       filter = private_message_filter(topic_query, inbox)
-      topic_query.options[:limit] = false
       topic_scope = topic_query.filter_private_message_new(current_user, filter)
     end
 
     topic_ids = TopicsBulkAction.new(
       current_user,
-      topic_scope.pluck(:id),
+      topic_scope.distinct(false).pluck(:id),
       type: "dismiss_topics"
     ).perform!
 
@@ -1246,7 +1245,11 @@ class TopicsController < ApplicationController
     if inbox = params[:private_message_inbox]
       filter = private_message_filter(topic_query, inbox)
       topic_query.options[:limit] = false
-      topics = topic_query.filter_private_messages_unread(current_user, filter)
+
+      topic_query
+        .filter_private_messages_unread(current_user, filter)
+        .distinct(false)
+        .pluck(:id)
     else
       topics = TopicQuery.unread_filter(topic_query.joined_topic_user, staff: guardian.is_staff?).listable_topics
       topics = TopicQuery.tracked_filter(topics, current_user.id) if params[:tracked].to_s == "true"
@@ -1265,9 +1268,9 @@ class TopicsController < ApplicationController
       if params[:tag_name].present?
         topics = topics.joins(:tags).where("tags.name": params[:tag_name])
       end
-    end
 
-    topics.pluck(:id)
+      topics.pluck(:id)
+    end
   end
 
   def private_message_filter(topic_query, inbox)