Expose types from useAPI

[MitchLillie]

Overview

We need a way to directly expose types for the APIs returned by useApi, for example navigation.navigate or saveMetafields.

Context

          @olavoasantos, @MitchLillie, there's still no easy way to expose this to the extensions (nor to web, for that matter).

I managed to resolve the type through some TS gymnastics like:

type ExtractElementType<T> = T extends readonly (infer ElementType)[]
  ? ElementType
  : never;

type ApiForRenderExtension = ReturnType<
  typeof useApi<'admin.settings.order-routing-rule.render'>
>;

type ExtractMethod<T extends keyof ApiForRenderExtension> =
  ApiForRenderExtension[T];

type SaveMetafields = ExtractMethod<'saveMetafields'>;

type MetafieldChange = ExtractElementType<Parameters<SaveMetafields>[0]>;

I like how the types are clean and properly derived from useApi(TARGET), but wondering if we'd want to expose some of the helpers that already exist in this repo as well in order to make this slightly simpler... or to allow for some sort of additional types 🤔

Normally one wouldn't need this, but as things grow, types might be needed in files that do not call useApi making some of this necessary 🤔

Originally posted by @jbalsas in #1472 (comment)