User bumpStamp if it is present

src/stores/room-list/algorithms/tag-sorting/RecentAlgorithm.ts

@@ -69,6 +69,12 @@ const getLastTs = (r: Room, userId: string): number => {
         if (!r?.timeline) {
             return Number.MAX_SAFE_INTEGER;
         }
+        // MSC4186: Simplified Sliding Sync sets this.
+        // If it's present, sort by it.
+        const bumpStamp = r.getBumpStamp();
+        if (bumpStamp) {
+            return bumpStamp;
+        }
 
         // If the room hasn't been joined yet, it probably won't have a timeline to
         // parse. We'll still fall back to the timeline if this fails, but chances