Mark forwarding implementation deprecated instead of deleting

We want to keep the old behavior until the old usages are removed.

Author: ejona86

interop-testing/src/main/java/io/grpc/testing/integration/RpcBehaviorLoadBalancerProvider.java

@@ -110,6 +110,14 @@ protected LoadBalancer delegate() {
       return delegateLb;
     }
 
+    @Deprecated
+    @Override
+    public void handleResolvedAddresses(ResolvedAddresses resolvedAddresses) {
+      helper.setRpcBehavior(
+          ((RpcBehaviorConfig) resolvedAddresses.getLoadBalancingPolicyConfig()).rpcBehavior);
+      delegateLb.handleResolvedAddresses(resolvedAddresses);
+    }
+
     @Override
     public Status acceptResolvedAddresses(ResolvedAddresses resolvedAddresses) {
       helper.setRpcBehavior(