FEATURE: Reintroduce better thread reply counter cache (#21197)

This was reverted in 38cebd3ed509524ad635adb107163d0496d0c550.
The issue was that I was using Discourse.redis.delete_prefixed
which does a slow redis KEYS lookup, which is not advised in
production. This commit removes that, and also ensures the periodical
thread count update only happens if threading is enabled.

I changed to use a redis INCR/DECR for reply count
cache. This avoids a round trip to redis to GET the current
count, and also avoids multi-process issues, where
if there's two processes trying to increment at the
same time, they may both receive the same value, add one
to it, then both write the same value back.
Then, it's only n+1 instead of n+2.

This also prevents almost all chat scheduled jobs from
running if chat is disabled, the only one remaining is
the message retention job.

plugins/chat/app/controllers/chat/api/channel_messages_controller.rb

@@ -4,4 +4,10 @@ class Chat::Api::ChannelMessagesController < Chat::ApiController
   def destroy
     with_service(Chat::TrashMessage) { on_model_not_found(:message) { raise Discourse::NotFound } }
   end
+
+  def restore
+    with_service(Chat::RestoreMessage) do
+      on_model_not_found(:message) { raise Discourse::NotFound }
+    end
+  end
 end

plugins/chat/app/controllers/chat/chat_controller.rb

@@ -12,8 +12,7 @@ module Chat
     # these endpoints require a standalone find because they need to be
     # able to get deleted channels and recover them.
     before_action :find_chatable, only: %i[enable_chat disable_chat]
-    before_action :find_chat_message,
-                  only: %i[delete restore lookup_message edit_message rebake message_link]
+    before_action :find_chat_message, only: %i[lookup_message edit_message rebake message_link]
     before_action :set_channel_and_chatable_with_access_check,
                   except: %i[
                     respond
@@ -233,18 +232,6 @@ module Chat
       render json: success_json
     end
 
-    def restore
-      chat_channel = @message.chat_channel
-      guardian.ensure_can_restore_chat!(@message, chat_channel.chatable)
-      updated = @message.recover!
-      if updated
-        Chat::Publisher.publish_restore!(chat_channel, @message)
-        render json: success_json
-      else
-        render_json_error(@message)
-      end
-    end
-
     def rebake
       guardian.ensure_can_rebake_chat_message!(@message)
       @message.rebake!(invalidate_oneboxes: true)