Populate simulcast codec layers. (#2334)

Previously, it was done on read. Missed populating it on write
in the TrackInfo consolidation effort.

Fix by populating layers when adding pending track itself.
As all codecs will have same layers, clone the top level layers and add
it all codecs.

pkg/rtc/participant.go

@@ -1670,9 +1670,15 @@ func (p *ParticipantImpl) addPendingTrackLocked(req *livekit.AddTrackRequest) *l
 			continue
 		}
 		seenCodecs[mime] = struct{}{}
+
+		clonedLayers := make([]*livekit.VideoLayer, 0, len(req.Layers))
+		for _, l := range req.Layers {
+			clonedLayers = append(clonedLayers, proto.Clone(l).(*livekit.VideoLayer))
+		}
 		ti.Codecs = append(ti.Codecs, &livekit.SimulcastCodecInfo{
 			MimeType: mime,
 			Cid:      codec.Cid,
+			Layers:   clonedLayers,
 		})
 	}