chore: improve typings

[layershifter]

This PR:

• add types for useShadowRoot & createProxy (required as you can't use existing exports)
  

  ReactShadow/src/index.js

  Lines 8 to 12 in a8a6ecd

  	export function useShadowRoot() {
  	return useContext(utils.Context);
  	}
  	export function createProxy(

• exports Root type (can be optional)

[Wildhoney]

Thanks!