sliding sync: add invited|joined_count

This is critical for calculating client-side push rules correctly.
Without it, the push processor may think rooms have a different
number of members, resulting typically in annoying failure modes
where rooms constantly make noises because the code thinks they
are 1:1 rooms.

src/sliding-sync.ts

@@ -84,6 +84,8 @@ export interface MSC3575RoomData {
     timeline: (IRoomEvent | IStateEvent)[];
     notification_count?: number;
     highlight_count?: number;
+    joined_count?: number;
+    invited_count?: number;
     invite_state?: IStateEvent[];
     initial?: boolean;
     limited?: boolean;