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
!disableSourceMaps;
  const skipBabel = bundleDefines.SKIP_BABEL;
  
  
  
  
  const babelExcludes = [
    "node_modules[\\\\\\/]core-js",
    "node_modules[\\\\\\/]web-streams-polyfill",
  ];
  if (enableSourceMaps) {
    babelExcludes.push("src[\\\\\\/]core[\\\\\\/](glyphlist|unicode)");
  }
  const babelExcludeRegExp = new RegExp(`(${babelExcludes.join("|")})`);
  
  
  
  const babelPlugins = [
    "@babel/plugin-transform-modules-commonjs",
    [
      "@babel/plugin-transform-runtime",
      {
        helpers: false,
        regenerator: true,
      },
    ],
  ];
  if (!bundleDefines.MOZCENTRAL && !bundleDefines.TESTING) {
    babelPlugins.push("@babel/plugin-proposal-logical-assignment-operators");
  }