Scroll replayer iframe on firstFullsnapshot (#451)

src/replay/index.ts

@@ -236,6 +236,9 @@ export class Replayer {
         this.rebuildFullSnapshot(
           firstFullsnapshot as fullSnapshotEvent & { timestamp: number },
         );
+        this.iframe.contentWindow!.scrollTo(
+          (firstFullsnapshot as fullSnapshotEvent).data.initialOffset,
+        );
       }, 1);
     }
   }