Typescript support

[Samywamy10]

Hey, it'd be super helpful to have this project (or at least /src/render/react/*) exported with full Typescript type definitions. This will help when writing the React code in knowing what widgets exist and which props they have (eg which styles are available) without needing to consult the docs/building and realising you've made a typo etc.

Keen to get your views on whether this would be helpful or not :).

I'm partly creating this issue to see if anything already exists, otherwise will look to add Typescript support with minimal modifications to existing logic