This field is only to be used in the Server-Server API, and not the
Client-Server API, but was being leaked when a federation response
was used in the /hierarchy API.
...and various code supporting it.
The /spaces endpoint was from an old version of MSC2946 and included
both a Client-Server and Server-Server API. Note that the unstable
/hierarchy endpoint (from the final version of MSC2946) is not yet
removed.
By returning all of the m.space.child state of the space, not just
the first 50. The number of rooms returned is still capped at 50.
For the federation API this implies that the requesting server will
need to individually query for any other rooms it is not joined to.
This updates the ordering of the returned events from the spaces
summary API to that defined in MSC2946 (which updates MSC1772).
Previously a step was skipped causing ordering to be inconsistent with
clients.
