Related to  #11474 and #12815.

The following should be added to `package.json` of `pdfjs-dist` for `worker-loader`.
```
  "peerDependenciesMeta": {
    "worker-loader": {
      "optional": true
    }
  }
```

npm v7 installs `peerDependencies` by default. We can see that calling `npm install pdfjs-dist` in an empty directory will install `webpack` and others in `node_modules`.

> In npm versions 3 through 6, peerDependencies were not automatically installed, and would raise a warning if an invalid version of the peer dependency was found in the tree. As of npm v7, peerDependencies are installed by default.

- https://docs.npmjs.com/cli/v7/configuring-npm/package-json#peerdependencies
- https://github.blog/2020-10-13-presenting-v7-0-0-of-the-npm-cli/

We can make `worker-loader` optional with `peerDependenciesMeta`.

- https://docs.npmjs.com/cli/v7/configuring-npm/package-json#peerdependenciesmeta
- https://github.com/npm/rfcs/issues/221
dir + "/build/pdf.min.js",
    (await Terser.minify(pdfFile, options)).code
  );
  fs.writeFileSync(
    dir + "/build/pdf.worker.min.js",
    (await Terser.minify(pdfWorkerFile, options)).code
  );
  fs.writeFileSync(
    dir + "/build/pdf.sandbox.min.js",
    (await Terser.minify(pdfSandboxFile, options)).code
  );
  fs.writeFileSync(
    dir + "image_decoders/pdf.image_decoders.min.js",
    (await Terser.minify(pdfImageDecodersFile, options)).code
  );
  console.log();
  console.log("### Cleaning js files");
  fs.unlinkSync(dir + "/web/viewer.js");
  fs.unlinkSync(dir + "/web/debugger.js");
  fs.unlinkSync(dir + "/build/pdf.js");
  fs.unlinkSync(dir + "/build/pdf.worker.js");
  fs.unlinkSync(dir + "/build/pdf.sandbox.js");
  fs.renameSync(dir + "/build/pdf.min.js", dir + "/build/pdf.js");
  fs.renameSync(dir + "/build/pdf.worker.min.js", dir + "/build/pdf.worker.js");
  fs.renameSync(
    dir + "/build/pdf.sandbox.min.js",
    dir + "/build/pdf.sandbox.js"
  );
  fs.renameSync(
    dir + "/image_decoders/pdf.image_decoders.min.js",