Add room heroes to RoomSubscription

[pixlwave]

Now that matrix-org/sliding-sync#304 has been merged, there's a new parameter that can be included on RoomSubscription - include_heroes: Bool which will in turn include the heroes in the sync response.

[Hywan]

Implementation inside Ruma is here, ruma/ruma#1691.

[Hywan]

Implementation inside the SDK, #3441.

[Hywan]

Another PR in Ruma, ruma/ruma#1818

[stefanceriu]

Closing this ar per the above ^

[Hywan]

Closed by #3461

[pixlwave]

Reopening this issue, as whilst looking at exposing these properties through the FFI, I noticed that the heroes stored in the SDK are missing their avatar URLs.

It would be great to have access to these as there are future designs where small rooms without an avatar_url will show a cluster of user avatars in Element X, and it would be really helpful to write the code with this in mind whilst fixing element-hq/element-x-ios#1659.

[pixlwave]

Note: from what I can tell, this solution of storing an array of IDs and a separate array of display names would probably need to switch to storing a single array of heroes instead.

[bnjbvr]

If by heroes you mean a tuple of user_id / optional user name / optional avatar URL, then yes, agreed with you; I just found out the proxy may return the avatar URLs there too. We need to not call this field heroes, though, to avoid conflicts with previous version of the data format where heroes existed. Are you willing to implement this?

[pixlwave]

Sure, I'm happy to give it a go whilst I'm here 👍