[Node.js package] Add TypeScript type definitions

[TejasQ]

Hello, I added type definitions for this project to https://github.com/DefinitelyTyped/DefinitelyTyped/pull/67445, enabling users to npm install @types/vosk into TypeScript applications and getting type definitions through that.

The only thing required here is an approval (or comment of approval) on that pull request from a maintainer of this project. If we can get that in, we can merge this. :)

[nshmyrev]

sure, probably it would be nice. Btw, we have a pull request about typescript here:

https://github.com/alphacep/vosk-api/pull/546

[TejasQ]

Wow, that's been open since 2021. 😨 I wonder which one we'll merge sooner. 😋