Add support for opening usercards by ID

[Mm2PL]

Description

Syntax is: /usercard #117691339.

Technically maybe enables @#117691339 to be a link to my user if it ever matches.

[kornes]

one issue, but works good 👍

[Nerixyz]

When entering a nonexistent ID, the ID will display in the name with the hash. But this isn't any different from before, so not an issue. 👍

[pajlada]

I would rather see this be a separate command, similar to /banid

[Felanbird]

I disagree realistically banid should have never been a separate command anyway

[pajlada]

Second attempt: I dislike the # prefix - it's already used for channels for IRC. Can we be explicit and use id:? (e.g. /usercard id:11148817)

[Felanbird]

Yeaaaaaaaaaah, it's unfortunate that IRC uses # since it's seems obviously correct for #USERID

[Mm2PL]

I could actually allow both prefixes and not complicate the code that much. As for it being a separate command, that could work although it's not something I'd like. As felanbird said, it shouldn't need to be a separate command.

[pajlada]

#4945 implements this for /ban and /timeout using id: prefix, with unit tests so it can be re-used for further commands (like this one) in the future.
I don't think allowing both id: and # is a good idea, so just id: as done in my PR above is my preferred way forward