PERF: cook message in background (#24227)

This commit starts from a simple observation: cooking messages on the hot path can be slow. Especially with a lot of mentions.

To move cooking from the hot path, this commit has made the following changes:

- updating cooked, inserting mentions and notifying user of new mentions has been moved inside the `process_message` job. It happens right after the `Chat::MessageProcessor` run, which is where the cooking happens.
- the similar existing code in `rebake!` has also been moved to rely on the `process_message`job only
- refactored `create_mentions` and `update_mentions` into one single `upsert_mentions` which can be called invariably
- allows services to decide if their job is ran inline or later. It avoids to need to know you have to use `Jobs.run_immediately!` in this case, in tests it will be inline per default
- made various frontend changes to make the chat-channel component lifecycle clearer. we had to handle `did-update @channel` which was super awkward and creating bugs with listeners which the changes of the PR made clear in failing specs
- adds a new `-processed` (and `-not-processed`) class on the chat message, this is made to have a good lifecyle hook in system specs

plugins/chat/spec/plugin_helper.rb

@@ -8,7 +8,7 @@ module ChatSystemHelpers
     user.activate
 
     SiteSetting.chat_enabled = true
-    SiteSetting.chat_allowed_groups = Group::AUTO_GROUPS[:trust_level_1]
+    SiteSetting.chat_allowed_groups = Group::AUTO_GROUPS[:everyone]
 
     channels_for_membership.each do |channel|
       membership = channel.add(user)
@@ -42,11 +42,11 @@ module ChatSystemHelpers
           in_reply_to_id: in_reply_to,
           thread_id: thread_id,
           guardian: last_user.guardian,
-          message: Faker::Lorem.paragraph,
+          message: Faker::Lorem.words(number: 5).join(" "),
         )
 
       raise "#{creator.inspect_steps.inspect}\n\n#{creator.inspect_steps.error}" if creator.failure?
-      last_message = creator.message
+      last_message = creator.message_instance
     end
 
     last_message.thread.set_replies_count_cache(messages_count - 1, update_db: true)
@@ -67,6 +67,19 @@ module ChatSpecHelpers
             "Service failed, see below for step details:\n\n" + result.inspect_steps.inspect,
           )
   end
+
+  def update_message(message, text: nil, user: Discourse.system_user, upload_ids: nil)
+    result =
+      Chat::UpdateMessage.call(
+        guardian: user.guardian,
+        message_id: message.id,
+        upload_ids: upload_ids,
+        message: text,
+        process_inline: true,
+      )
+    service_failed!(result) if result.failure?
+    result.message_instance
+  end
 end
 
 RSpec.configure do |config|