Allow fetching all room state events of a given type

[ulope]

Related to: matrix-org/matrix-spec-proposals#3675

Requested Feature

Please add an endpoint to query room state events of a given type without having to give a state key as well.

Background

There already exists the GET /_matrix/client/r0/rooms/{roomId}/state/{eventType}/{stateKey} endpoint which allows fetching specific eventTypes for a room where the stateKey is known.

One use case where the stateKey is (in the general case) not knowable is fetching room aliases. Therefore it's currently necessary to use the generic GET /_matrix/client/r0/rooms/{roomId}/state/ endpoint which can produce quite large responses for big rooms.

[richvdh]

that would be a spec feature first and foremost; matrix-doc is the place to raise it.

Note that your stated usecase would be made redundant by matrix-org/matrix-spec-proposals#2432. (It's not possible to reliably get a list of aliases for a room by looking at the aliases events anyway, see https://github.com/matrix-org/matrix-doc/issues/2262)