Encapsulate more common code to CUDAESProduct

[makortel]

From @fwyzard in https://github.com/cms-patatrack/cmssw/pull/301/files#r279369606

The pattern seems to be:

• start with a class/struct for the actual data on th GPU

  Payload *cablingMapHost = nullptr; // pointer to struct in CPU

• define a wrapper

  struct PayloadWrapper {
    ~PayloadWrapper();
    Payload *payload = nullptr; // pointer to struct in GPU
  };

• add a CUDAESProduct data mamber:

  CUDAESProduct<PayloadWrapper> payload_;

• produce it for the gpu like this

Payload const* getGPUProductAsync(cuda::stream_t<>& cudaStream) const {
  const auto& data = payload_.dataForCurrentDeviceAsync(cudaStream, [this](PayloadWrapper& data, cuda::stream_t<>& stream) {
      // allocate
      cudaCheck(cudaMalloc(&data.payload, sizeof(Payload)));

      // transfer
      cudaCheck(cudaMemcpyAsync(data.payload, this->cablingMapHost, sizeof(Payload), cudaMemcpyDefault, stream.id()));
  });
  return data.payload;
}

Would it make sense to encapsulate more of the common part into CUDAESProduct ?

And/or to drop the PayloadWrapper in favour of a unique_ptr, possibly with a custom destructor ?