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
"wintersmith",
    ghPagesGit
  )
);
function packageBowerJson() {
  const VERSION = getVersionJSON().version;
  const DIST_NAME = "pdfjs-dist";
  const DIST_DESCRIPTION = "Generic build of Mozilla's PDF.js library.";
  const DIST_KEYWORDS = ["Mozilla", "pdf", "pdf.js"];
  const DIST_HOMEPAGE = "http://mozilla.github.io/pdf.js/";
  const DIST_BUGS_URL = "https://github.com/mozilla/pdf.js/issues";
  const DIST_LICENSE = "Apache-2.0";
  const npmManifest = {
    name: DIST_NAME,
    version: VERSION,
    main: "build/pdf.js",
    types: "types/src/pdf.d.ts",
    description: DIST_DESCRIPTION,
    keywords: DIST_KEYWORDS,
    homepage: DIST_HOMEPAGE,
    bugs: DIST_BUGS_URL,
    license: DIST_LICENSE,
    peerDependencies: {
      "worker-loader": "^3.0.7", 
    },
    browser: {
      canvas: false,
      fs: false,
      http: false,
      https: false,