Propagate original picker call started event

Author: murgatroid99

packages/grpc-js-xds/src/load-balancer-eds.ts

@@ -217,6 +217,7 @@ export class EdsLoadBalancer implements LoadBalancer {
                 status: originalPick.status,
                 subchannel: originalPick.subchannel,
                 onCallStarted: () => {
+                  originalPick.onCallStarted?.();
                   this.concurrentRequests += 1;
                 },
                 extraFilterFactory: extraFilterFactory