SSS: implement room account data

src/api/client_server/sync/msc4186.rs

@@ -484,9 +484,27 @@ pub(crate) async fn sync_events_v5_route(
             })
             .collect();
 
+        let mut rooms_account_data = BTreeMap::new();
+        for (room_id, todo_room) in &todo_rooms {
+            let account_data: Vec<_> = services()
+                .account_data
+                .room_changes_since(&sender_user, room_id, todo_room.roomsince)?
+                .into_iter()
+                .map(|(event_type, content)| {
+                    account_data::raw_room_event_from_parts(
+                        &event_type,
+                        &content,
+                    )
+                })
+                .collect();
+            if !account_data.is_empty() {
+                rooms_account_data.insert(room_id.clone(), account_data);
+            }
+        }
+
         Some(sync_events::v5::response::AccountData {
             global,
-            rooms: BTreeMap::new(),
+            rooms: rooms_account_data,
         })
     } else {
         None