Support server and friend nicknames in chat bar mention autocomplete

Problem

Right now, users can't use the chat bar autocomplete to find and mention someone by their server nickname or friend nickname. The autocomplete only matches against usernames which causes inconvenience in communities where people primarily go by server-specific names, or when a user has set a personal alias for a friend to remember them easier.

Proposed solution

Update the chat bar autocomplete logic to search username, server nickname, and friend nickname. When typing @ followed by characters in the chat box, the autocomplete dropdown should suggest users if the typed text matches any of these three display names.