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
const imageDecodersAMDName = "pdfjs-dist/image_decoders/pdf.image_decoders";
  const imageDecodersOutputName = "pdf.image_decoders.js";
  const componentsFileConfig = createWebpackConfig(defines, {
    filename: imageDecodersOutputName,
    library: imageDecodersAMDName,
    libraryTarget: "umd",
    umdNamedDefine: true,
  });
  return gulp
    .src("./src/pdf.image_decoders.js")
    .pipe(webpack2Stream(componentsFileConfig))
    .pipe(replaceWebpackRequire())
    .pipe(replaceJSRootName(imageDecodersAMDName, "pdfjsImageDecoders"));
}
function createCMapBundle() {
  return gulp.src(["external/bcmaps/*.bcmap", "external/bcmaps/LICENSE"], {
    base: "external/bcmaps",
  });
}
function createStandardFontBundle() {