appservice: Rename virtual user to appservice user

[johannescpk]

Currently the appservice crate calls the users for which identity assertion is performed "virtual users". There's no clear terminology how those users are called in the spec. The homeserver itself just sees them as users belonging to a specific appservice. So it would make sense to just call them users in the scope of the appservice crate, which would also remove the confusion around the difference of "virtual users" (identity assertion) and the "main user" (sender_localpart).

[jplatte]

There's also the option of renaming to puppet_user, which I think is more common terminology for users in an appservice's namespace.

[Yoric]

They're not really users, though, until they have been registered, right? So I suspect that just calling them "users" would be misleading.

I have no problem with "virtual user" or "puppet user", as long as there is something making it clear that it's not completely a user out of the box.

[johannescpk]

"Puppet" is an ecosystem term, not something in the spec – and the sender_localpart user isn't a puppet.

"virtual user" is mentioned twice in the spec, but it collides with the sender_localpart user, which isn't a virtual user. Both are appservice users.

Hence the most fitting term is "appservice user", which makes it just "user" in the context of the appservice crate.

[Half-Shot]

Agree with @johannescpk. The other terms are more bridge terms than AS terms. I would call them appservice users.