DEV: Use UploadReference instead of ChatUpload in chat (#19947)

We've had the UploadReference table for some time now in core,
but it was added after ChatUpload was and chat was just never
moved over to this new system.

This commit changes all chat code dealing with uploads to create/
update/delete/query UploadReference records instead of ChatUpload
records for consistency. At a later date we will drop the ChatUpload
table, but for now keeping it for data backup.

The migration + post migration are the same, we need both in case
any chat uploads are added/removed during deploy.

plugins/chat/lib/chat_message_updater.rb

@@ -83,7 +83,8 @@ class Chat::ChatMessageUpdater
   def update_uploads(upload_info)
     return unless upload_info[:changed]
 
-    ChatUpload.where(chat_message: @chat_message).destroy_all
+    DB.exec("DELETE FROM chat_uploads WHERE chat_message_id = #{@chat_message.id}")
+    UploadReference.where(target: @chat_message).destroy_all
     @chat_message.attach_uploads(upload_info[:uploads])
   end
 

plugins/chat/lib/chat_transcript_service.rb

@@ -147,7 +147,7 @@ class ChatTranscriptService
   def messages
     @messages ||=
       ChatMessage
-        .includes(:user, chat_uploads: :upload)
+        .includes(:user, upload_references: :upload)
         .where(id: @message_ids, chat_channel_id: @channel.id)
         .order(:created_at)
   end

plugins/chat/lib/message_mover.rb

@@ -125,10 +125,10 @@ class Chat::MessageMover
     SQL
 
     DB.exec(<<~SQL)
-      UPDATE chat_uploads cu
-      SET chat_message_id = mm.new_chat_message_id
+      UPDATE upload_references uref
+      SET target_id = mm.new_chat_message_id
       FROM moved_chat_messages mm
-      WHERE cu.chat_message_id = mm.old_chat_message_id
+      WHERE uref.target_id = mm.old_chat_message_id AND uref.target_type = 'ChatMessage'
     SQL
 
     DB.exec(<<~SQL)