Pretty-print tfds.features.FeaturesDict.

def _pprint_features_dict(features_dict, indent=0, add_prefix=True):
  """Pretty-print tfds.features.FeaturesDict."""
  first_last_indent_str = " " * indent
  indent_str = " " * (indent + 4)
  first_line = "%s%s({" % (
      first_last_indent_str if add_prefix else "",
      type(features_dict).__name__,
  )
  lines = [first_line]
  for k in sorted(list(features_dict.keys())):
    v = features_dict[k]
    if isinstance(v, tfds.features.FeaturesDict):
      v_str = _pprint_features_dict(v, indent + 4, False)
    else:
      v_str = str(v)
    lines.append("%s'%s': %s," % (indent_str, k, v_str))
  lines.append("%s})" % first_last_indent_str)
  return "\n".join(lines)