feat: de-experiment google-c2p resolver (#1896)

* feat: de-experiment google-c2p resolver * docs: added comment about c2p Co-authored-by: Tomo Suzuki <suztomo@google.com>

Author: mohanli-ml

gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java

@@ -326,9 +326,10 @@ && isOnComputeEngine()) {
  GoogleDefaultChannelCredentials.newBuilder().callCredentials(callCreds).build();
  isDirectPathXdsEnabled = Boolean.parseBoolean(envProvider.getenv(DIRECT_PATH_ENV_ENABLE_XDS));
  if (isDirectPathXdsEnabled) {
- // google-c2p resolver target must not have a port number
- builder =
- Grpc.newChannelBuilder("google-c2p-experimental:///" + serviceAddress, channelCreds);
+ // google-c2p: CloudToProd(C2P) Directpath. This scheme is defined in
+ // io.grpc.googleapis.GoogleCloudToProdNameResolverProvider.
+ // This resolver target must not have a port number.
+ builder = Grpc.newChannelBuilder("google-c2p:///" + serviceAddress, channelCreds);
  } else {
  builder = Grpc.newChannelBuilderForAddress(serviceAddress, port, channelCreds);
  builder.defaultServiceConfig(directPathServiceConfig);