Fix missing creators support using via (#2431)

* add additional_creators in IRoomCreateContent type

* use creators in getViaServers

* consider creators in guessing perfect parent

src/types/matrix/room.ts

@@ -70,6 +70,7 @@ export type IRoomCreateContent = {
   ['m.federate']?: boolean;
   room_version: string;
   type?: string;
+  additional_creators?: string[];
   predecessor?: {
     event_id?: string;
     room_id: string;