Typings not being resolved for webpack.config.ts

When configuring webpack with a [webpack.config.**ts**](https://github.com/aurelia-contrib/aurelia-router-metadata/blob/master/webpack.config.ts) rather than a webpack.config.**js**, the typings are not properly resolved:


Everything **works**, it's just this error and the lack of typings/intellisense that makes the experience suboptimal.

I wouldn't mind submitting a PR if this is indeed a "bug", but I just want to make sure first that there's not some kind of setting that I'm missing.

Start by inspecting webpack.config.ts and the repository's TypeScript and webpack configuration to determine why typings and IntelliSense are missing while bundling still works. Done means the configuration produces no typings-resolution error and exposes the expected typings in the editor; verify this using the reported setup.

Written by the indexing model from the issue text.