feat: Added helping generic types for hooks

[lucasconstantino]

When using TypeScript and code generation tools for GraphQL query typings, the use of hooks such as useQuery can become very bloated with long generics, and what should probably a simple one liner gets quite hard to read, specially with multiple hooks (many mutations, for instance).

No TypeScript:

import { useQuery } from '@apollo/react-hooks'

const HelloWorld = ({ name }) => {
  const { data, loading } = useQuery(HELLO_WORLD_QUERY, { variables: { name } })

  return loading ? 'loading' : <p>{data.hello}</p>
}

Typescript:

import { useQuery } from '@apollo/react-hooks'

import {
  HELLO_WORLD_QUERY_DATA,
  HELLO_WORLD_QUERY_VARIABLES,
} from './generated-types'

const HelloWorld: React.FC<{ name: string }> = ({ name }) => {
  const { data, loading } = useQuery<
    HELLO_WORLD_QUERY_DATA,
    HELLO_WORLD_QUERY_VARIABLES
  >(HELLO_WORLD_QUERY, { variables: { name } })

  return loading ? 'loading' : <p>{data.hello}</p>
}

What this pull-request does is export a generic type to allow typing of queries/mutations before we use hooks. Outcome could be something like this:

TypeScript with UseQuery/UseMutation/UseSubscription:

import { useQuery, UseQuery } from '@apollo/react-hooks'

import {
  HELLO_WORLD_QUERY_DATA,
  HELLO_WORLD_QUERY_VARIABLES,
} from './generated-types'

const useHelloWorld: UseQuery<
  HELLO_WORLD_QUERY_DATA,
  HELLO_WORLD_QUERY_VARIABLES
> = useQuery

const HelloWorld: React.FC<{ name: string }> = ({ name }) => {
  const { data, loading } = useHelloWorld(HELLO_WORLD_QUERY, { variables: { name } })

  return loading ? 'loading' : <p>{data.hello}</p>
}

As can be seen, this makes it easier to reduce complexity and code within the component itself, while moving static non-variable procedures such as typing outside the business code.

Ps.: some may say this is already possible by creating a secondary hook, which is a similar solution, but the solution with helper types guarantees we have same APIs available with no need to create new interfaces due to custom hooks argument types.