Feature request: Allow augmentation to accept parsed typeDefs from 'gql' tag

[michaeldgraham]

Currently, the schema augmentation functions only accept typeDefs in the format of a string containing SDL. This issue requests support for passing parsed typeDefs to the augmentation functions. This occurs, for example, when a gql tag is applied on typeDefs:

import { gql } from "apollo-server";

const typeDefs = gql`
  type User {
    id: ID!
    username: String
  }
`;