code: public static String deprecatedToString(Object deprecatedProp) {
      boolean emptyDeprecated = (deprecatedProp == null);
      if (emptyDeprecated) {
        return "";
      } else if (deprecatedProp instanceof String) {
        return "@available(*, deprecated, message=\"" + deprecatedProp + "\")";
      } else {
        return "@available(*, deprecated)";
      }
    }
docs: Return a deprecated attribute, as a string of Swift source.
  @param deprecatedProp provides the deprecated Pegasus schema property, if any.  May be a
  Boolean, a String, or null.
  
  @return a Swift property indicating that a type or field is deprecated.