FIX: Topic user bookmarked column is out of sync after post moves (#12612)

When posts are moved from one topic to another, the `topic_user.bookmarked` column for all users in the new and the old topic needs to be resynced, for example because a user bookmarks post 12 in topic 1, then it is moved to topic 2, the topic_user record for topic 1 should no longer be bookmarked. A background job has been added to sync the column for a specified topic, or for no topic at all, which does it for all topics like the migration.

Also includes a migration that we have run in the past to fix bad data.

----

This has been addressed in other places in the past:

https://github.com/discourse/discourse/pull/10211
https://github.com/discourse/discourse/pull/10188

db/migrate/20210406060434_fix_topic_user_bookmarked_sync_issues_again.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+class FixTopicUserBookmarkedSyncIssuesAgain < ActiveRecord::Migration[6.0]
+  disable_ddl_transaction!
+
+  def up
+    DB.exec(
+      <<~SQL
+        UPDATE topic_users SET bookmarked = true
+        FROM bookmarks AS b
+        WHERE NOT topic_users.bookmarked AND topic_users.topic_id = b.topic_id AND topic_users.user_id = b.user_id
+      SQL
+    )
+
+    DB.exec(
+      <<~SQL
+        UPDATE topic_users SET bookmarked = false
+        WHERE topic_users.bookmarked AND (SELECT COUNT(*) FROM bookmarks WHERE topic_id = topic_users.topic_id AND user_id = topic_users.user_id) = 0
+      SQL
+    )
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end