Add new room membership APIs

[erikjohnston]

Add two new APIs:

• /joined_rooms that returns the list of rooms the user is in
• /room/<room_id>/joined_members that returns the list of currently joined users and their profile data

These are primarily designed for ASes that may want to efficiently look up those pieces of information without otherwise needing to do a full /sync

---

Example output:

GET /joined_rooms

{"joined_rooms": ["!foo:example.com"]}

GET /room/!foo:example.com/joined_members

{"joined": {"@bar:example.com": { "display_name": "Bar", "avatar_url": null }}}

[erikjohnston]

matrix-org/sytest#329

[NegativeMjark]

LGTM

[leonerd]

I admit it's probably a bit late now, but is there any reason why

{"joined": {"@bar:example.com": { "display_name": "Bar", "avatar_url": null }}}

the toplevel key is joined? This is neither the last component of the URI (joined_members), nor is it the actual membership string value (which would be join).

[t3chguy]

Correction: GET /rooms/!foo:example.com/joined_members
s/room/rooms/