How to use the @stryker-mutator/util.fsAsPromised.readdirSync function in @stryker-mutator/util

this.pluginDescriptors.forEach(pluginExpression => {
      if (typeof pluginExpression === 'string') {
        if (pluginExpression.includes('*')) {
          // Plugin directory is the node_modules folder of the module that installed stryker
          // So if current __dirname is './@stryker-mutator/core/src/di' so 4 directories above
          const pluginDirectory = path.dirname(path.resolve(__dirname, '..', '..', '..', '..', pluginExpression));
          const regexp = new RegExp('^' + path.basename(pluginExpression).replace('*', '.*'));

          this.log.debug('Loading %s from %s', pluginExpression, pluginDirectory);
          const plugins = fsAsPromised
            .readdirSync(pluginDirectory)
            .filter(pluginName => !IGNORED_PACKAGES.includes(pluginName) && regexp.test(pluginName))
            .map(pluginName => path.resolve(pluginDirectory, pluginName));
          if (plugins.length === 0) {
            this.log.debug('Expression %s not resulted in plugins to load', pluginExpression);
          }
          plugins
            .map(plugin => {
              this.log.debug('Loading plugin "%s" (matched with expression %s)', plugin, pluginExpression);
              return plugin;
            })
            .forEach(p => modules.push(p));
        } else {
          modules.push(pluginExpression);
        }
      } else {

this.pluginDescriptors.forEach(pluginExpression => {
      if (_.isString(pluginExpression)) {
        if (pluginExpression.indexOf('*') !== -1) {

          // Plugin directory is the node_modules folder of the module that installed stryker
          // So if current __dirname is './stryker/src/di' so 3 directories above
          const pluginDirectory = path.resolve(__dirname, '..', '..', '..');
          const regexp = new RegExp('^' + pluginExpression.replace('*', '.*'));

          this.log.debug('Loading %s from %s', pluginExpression, pluginDirectory);
          const plugins = fsAsPromised.readdirSync(pluginDirectory)
            .filter(pluginName => IGNORED_PACKAGES.indexOf(pluginName) === -1 && regexp.test(pluginName))
            .map(pluginName => pluginDirectory + '/' + pluginName);
          if (plugins.length === 0) {
            this.log.debug('Expression %s not resulted in plugins to load', pluginExpression);
          }
          plugins
            .map(plugin => path.basename(plugin))
            .map(plugin => {
              this.log.debug('Loading plugins %s (matched with expression %s)', plugin, pluginExpression);
              return plugin;
            })
            .forEach(p => modules.push(p));
        } else {
          modules.push(pluginExpression);
        }
      } else {