Add type definition file

[cecilphillip]

I'm using this with Visual Studio Code and it would be great to explore the available API operations via the autocomplete of the editor. If there's a .d.ts file in the npm package, most editors should be able to enable this.

[gluons]

I really want it.

@types/webpack-chain is broken. No update for missing API for month.

Stuck in DefinitelyTyped/DefinitelyTyped#27519

[edmorley]

Hi! If someone was up for adding type definitions to the webpack-chain repository (along with validation of them in CI and an easy way to verify when developing locally), then we'd be happy to accept them :-)

[edmorley]

Released in webpack-chain v5.2.0:
https://www.npmjs.com/package/webpack-chain/v/5.2.0