`/joined_members` is not entirely clear about returning local room member objects

This was unclear, as conduit (accidentally) implemented it by returning global display-name/avatar information instead of room-local ones.

The spec says;

This API returns a map of MXIDs to member info objects for members of the room. The current user must be in the room for it to work, unless it is an Application Service in which case any of the AS's users must be in the room. This API is primarily for Application Services and should be faster to respond than /members as it can be implemented more efficiently on the server.

The relevant part is;

This API returns a map of MXIDs to member info objects for members of the room.

While this part may be reasonable on a double-take, I just wanted to note it here that it generated confusion (even for me, reading the first time) as what is exactly meant by that, in terms of returning room-local data vs global member data.

Start at the /joined_members definition in the Matrix specification and read the surrounding API text. Clarify that the returned member info objects contain room-local member data rather than global display-name or avatar data, while preserving the existing behavior and intent. Done means the wording cannot reasonably be read as referring to global member information.