Fetch metadata only using PyTorch Lite Model C++ API

FetchModelMetadata.cpp

#include <torch/csrc/jit/mobile/import.h>
#include <torch/csrc/jit/mobile/module.h>

int main() {
  std::string model_path = "AddTensorsModel.ptl";
  torch::jit::ExtraFilesMap extra_files;

  // Add keys into extra_files to indicate which metadata files
  // we wish to fetch.
  extra_files["model_info.txt"] = "";
  extra_files["dtype_info.txt"] = "";
  
  torch::jit::_load_extra_only_for_mobile(model_path, c10::nullopt, extra_files);
  
  for (auto it: extra_files) {
    std::cout << "Metadata [" << it.first << "]: " << it.second << std::endl;
  }
}