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
console.log();
  console.log("### Creating baseline environment");
  const baselineCommit = process.env.BASELINE;
  if (!baselineCommit) {
    done(new Error("Missing baseline commit. Specify the BASELINE variable."));
    return;
  }
  let initializeCommand = "git fetch origin";
  if (!checkDir(BASELINE_DIR)) {
    mkdirp.sync(BASELINE_DIR);
    initializeCommand = "git clone ../../ .";
  }
  const workingDirectory = path.resolve(process.cwd(), BASELINE_DIR);
  exec(initializeCommand, { cwd: workingDirectory }, function (error) {
    if (error) {
      done(new Error("Baseline clone/fetch failed."));
      return;
    }
    exec(
      "git checkout " + baselineCommit,
      { cwd: workingDirectory },
      function (error2) {
        if (error2) {
          done(new Error("Baseline commit checkout failed."));
          return;