This project is using internal-only protobuf APIs that may soon change namespaces or disappear.

Hi there, I work on protobufs. I noticed your project is using APIs from `google/protobuf/util/internal`:

```
#include "google/protobuf/util/internal/json_stream_parser.h"
#include "google/protobuf/util/internal/object_writer.h"
```

https://github.com/grpc-ecosystem/grpc-httpjson-transcoding/blob/master/src/json_request_translator.cc#L23-L24

These APIs have "internal" in the include path, and are not for end-user consumption. We will likely be removing these soon, or at least changing their namespace to make it even clearer that these APIs are not for users.

This came to my attention because of this PR in our repo:

https://github.com/protocolbuffers/protobuf/pull/5939#issuecomment-524411767