Be able to search "from:" a user ID instead of a name

Searching "from:ID" or "mentions:ID" both return results that *mention* a user with a specific ID. This functionality aligns with the "mentions:" prefix, but the prior would be exceedingly useful for keeping track of messages sent by a user that left a server. At the moment, a server moderator just do a lot of digging through history to find a specific user's messages if they don't exist on the server anymore.