function justTextHighlightResult(code) {
      const result = {
        value: escape(code),
        illegal: false,
        relevance: 0,
        _top: PLAINTEXT_LANGUAGE,
        _emitter: new options.__emitter(options)
      };
      result._emitter.addText(code);
      return result;
    }
returns a valid highlight result, without actually doing any actual work,
auto highlight starts with this and it's possible for small snippets that
auto-detection may not find a better match
@param {string} code
@returns {HighlightResult}