Turn Exported* protos with embedded metadata into a nested dict.

def _GetNestedDict(self, value):
    """Turn Exported* protos with embedded metadata into a nested dict."""
    row = {}
    for type_info in value.__class__.type_infos:
      # We only expect the metadata proto to be included as ProtoEmbedded.
      if type_info.__class__.__name__ == "ProtoEmbedded":
        row[type_info.name] = self._GetNestedDict(value.Get(type_info.name))
      else:
        row[type_info.name] = utils.SmartStr(value.Get(type_info.name))

    return row