RFC: Add helper function to get types of enums and scalars

[kitten]

Originally requested on Discord by @hazlad

Summary

One thing that I am missing is the ability to generate a string union type to represent all possible enum values - would this be something you'd consider adding to the library?

For example with the Pokemen example in the repo:

export type PokemonType = "Bug" | "Dark" | "Dragon" /* etc. */;

Proposed Solution

We should have a user accessible function, so, to keep things simple, a method on graphql, e.g. graphql.scalar() should be suitable.

This method should accept a scalar or enum name, and optionally a value, and should type check
said value against the allowable scalar/enum type.

The return type should be inferred to be the enum/scalar type (or a more exact one when a value is passed so ReturnType can be used to get the raw type.

Requirements

• We must be able to get the raw return type
  • e.g. ReturnType<typeof graphql.scalar('PokemonType')>
• We must be able to type check a value
  • e.g. graphql.scalar('Pokemontype', 'Bug')

[kitten]

This is now supported in v1.2.0 via #45.

Documentation for this is found on the API reference docs page: graphql.scalar()