[Feature Request] Allow specifying a root directory to resolve polyfill'ed modules against

[dmnsgn]

Issue:
At the moment, all resolution assumes the modules are installed alongside webpack.

The fallback configuration (https://webpack.js.org/configuration/resolve/#resolvefallback) allows absolute path to be specified: path.resolve(__dirname, 'path/to/file.js'). That's particularly useful if you run webpack programmatically and have the config in a different place than the codebase containing the polyfills.

Feature Request:

Add an option (root, resolutionDir, base, notSureWhatsAGoodName...) to specify the root. Either absolute or a function:

const myDir = path.resolve(__dirname, 'somewhere')
new NodePolyfillPlugin({
  root: (polyfillName) => path.join(myDir, polyfillName)
  // or...
  root: myDir,
})

[Richienb]

At the moment, all resolution assumes the modules are installed alongside webpack.

They are.

That's particularly useful if you run webpack programmatically and have the config in a different place than the codebase containing the polyfills.

In that case, it could be better to just detect where node-polyfill-webpack-plugin is installed and resolve the absolute path relative to the node_modules directory it is installed in.

[dmnsgn]

Could replacing assert: "assert", with assert: require.resolve("assert"), etc. help achieve that instead of using path?