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('Baseline commit "' + baselineCommit + '" checked out.');
        done();
      }
    );
  });
}
gulp.task(
  "unittestcli",
  gulp.series(setTestEnv, "lib-legacy", function runUnitTestCli(done) {
    const options = [
      "node_modules/jasmine/bin/jasmine",
      "JASMINE_CONFIG_PATH=test/unit/clitests.json",
    ];
    const jasmineProcess = startNode(options, { stdio: "inherit" });
    jasmineProcess.on("close", function (code) {
      if (code !== 0) {
        done(new Error("Unit tests failed."));
        return;
      }
      done();
    });
  })
);
gulp.task("lint", function (done) {
  console.log();
  console.log("### Linting JS/CSS files");
  
  const esLintOptions = [
    "node_modules/eslint/bin/eslint",