How to use the pn/fs.readdir function in pn

async _collectSources() {
    const stats = await Promise.all(this.sources.map(src => fs.stat(src.idlPath)));
    const files = [];
    for (let i = 0; i < stats.length; ++i) {
      if (stats[i].isDirectory()) {
        const folderContents = await fs.readdir(this.sources[i].idlPath);
        for (const file of folderContents) {
          if (file.endsWith(".webidl")) {
            files.push({
              idlPath: path.join(this.sources[i].idlPath, file),
              impl: this.sources[i].impl
            });
          }
        }
      } else {
        files.push({
          idlPath: this.sources[i].idlPath,
          impl: this.sources[i].impl
        });
      }
    }
    return files;