Support union type of object literal

[kohii]

Summary

Add support for union types of object.

e.g.

type NetworkLoadingState = {
  state: "loading";
};
type NetworkFailedState = {
  state: "failed";
  code: number;
};
type NetworkSuccessState = {
  state: "success";
  response: {
    title: string;
    duration: number;
    summary: string;
  };
};
// Create a type which represents only one of the above types
// but you aren't sure which it is yet.
type NetworkState =
  | NetworkLoadingState
  | NetworkFailedState
  | NetworkSuccessState;

Handbook - Unions and Intersection Types