FEATURE: Hook up chat bulk delete for threads (#21109)

Followup to bd5c5c4b5f,
this commit hooks up the bulk delete events for chat
messages inside the thread panel, by fanning out the
deleted message IDs based on whether they belong to
a thread or not.

Also adds a system spec to cover this case, as previously
the bulk delete event would have been broken with an incorrect
`typ` rather than `type` hash key.

plugins/chat/app/models/chat/thread.rb

@@ -34,6 +34,21 @@ module Chat
       original_message.excerpt(max_length: EXCERPT_LENGTH)
     end
 
+    def self.grouped_messages(thread_ids: nil, message_ids: nil, include_original_message: true)
+      DB.query(<<~SQL, message_ids: message_ids, thread_ids: thread_ids)
+        SELECT thread_id,
+          array_agg(chat_messages.id ORDER BY chat_messages.created_at, chat_messages.id) AS thread_message_ids,
+          chat_threads.original_message_id
+        FROM chat_messages
+        INNER JOIN chat_threads ON chat_threads.id = chat_messages.thread_id
+        WHERE thread_id IS NOT NULL
+        #{thread_ids ? "AND thread_id IN (:thread_ids)" : ""}
+        #{message_ids ? "AND chat_messages.id IN (:message_ids)" : ""}
+        #{include_original_message ? "" : "AND chat_messages.id != chat_threads.original_message_id"}
+        GROUP BY thread_id, chat_threads.original_message_id;
+      SQL
+    end
+
     def self.ensure_consistency!
       update_counts
     end