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
"--ext",
    ".js,.jsm,.json",
    ".",
    "--report-unused-disable-directives",
  ];
  if (process.argv.includes("--fix")) {
    esLintOptions.push("--fix");
  }
  const styleLintOptions = [
    "node_modules/stylelint/bin/stylelint",
    "**/*.css",
    "--report-needless-disables",
  ];
  if (process.argv.includes("--fix")) {
    styleLintOptions.push("--fix");
  }
  const esLintProcess = startNode(esLintOptions, { stdio: "inherit" });
  esLintProcess.on("close", function (esLintCode) {
    if (esLintCode !== 0) {
      done(new Error("ESLint failed."));
      return;
    }
    const styleLintProcess = startNode(styleLintOptions, { stdio: "inherit" });
    styleLintProcess.on("close", function (styleLintCode) {
      if (styleLintCode !== 0) {
        done(new Error("Stylelint failed."));
        return;
      }
      console.log("files checked, no errors found");
      done();