FEATURE: Better thread reply counter cache (#21108)

This commit introduces a redis cache over the top of the thread
replies_count DB cache, so that we can quickly and accurately
increment/decrement the reply count for all users and not have
to constantly update the database-level count. This is done so
the UI can have a count that is displayed to the users on each
thread indicator, that appears to live update on each chat
message create/trash/recover inside the thread.

This commit also introduces the `Chat::RestoreMessage` service
and moves the restore endpoint into the `Api::ChannelMessages`
controller as part of incremental migrations to move things out
of ChatController.

Finally, this commit refactors `Chat::Publisher` to be less repetitive
with its `MessageBus` sending code.

plugins/chat/config/routes.rb

@@ -30,6 +30,7 @@ Chat::Engine.routes.draw do
 
     get "/channels/:channel_id/threads/:thread_id" => "channel_threads#show"
 
+    put "/channels/:channel_id/messages/:message_id/restore" => "channel_messages#restore"
     delete "/channels/:channel_id/messages/:message_id" => "channel_messages#destroy"
   end
 
@@ -61,7 +62,6 @@ Chat::Engine.routes.draw do
   put "/:chat_channel_id/:message_id/rebake" => "chat#rebake"
   post "/:chat_channel_id/:message_id/flag" => "chat#flag"
   post "/:chat_channel_id/quote" => "chat#quote_messages"
-  put "/:chat_channel_id/restore/:message_id" => "chat#restore"
   get "/lookup/:message_id" => "chat#lookup_message"
   put "/:chat_channel_id/read/:message_id" => "chat#update_user_last_read"
   put "/user_chat_enabled/:user_id" => "chat#set_user_chat_status"