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
process.env.TESTING = "true";
  
  
  
  process.env.TZ = "UTC";
  done();
}
gulp.task(
  "test",
  gulp.series(setTestEnv, "generic", "components", function runTest() {
    return streamqueue(
      { objectMode: true },
      createTestSource("unit"),
      createTestSource("browser"),
      createTestSource("integration")
    );
  })
);
gulp.task(
  "bottest",
  gulp.series(setTestEnv, "generic", "components", function runBotTest() {
    return streamqueue(
      { objectMode: true },
      createTestSource("unit", true),
      createTestSource("font", true),
      createTestSource("browser (no reftest)", true),
      createTestSource("integration")
    );