Make classes and interfaces inherit GraphQL fields and interfaces from classes they extend and interfaces they implement

[captbaritone]

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/** @gqlType */
class Parent {
  /** @gqlField */
  parentField: string;
}

class Intermediate extends Parent {}

/** @gqlType */
export class Child extends Intermediate {
  /** @gqlField */
  childField: string;
}

Would now extract:

type Child {
  childField: String
  parentField: String
}

type Parent {
  parentField: String
}

This change also allows you to define GraphQL interfaces using TypeScript types.

TODO

• [ ] Documentation
• [x] Integration tests
• [ ] Validate/test method resolution order
• [x] Don't use private methods/properties of the typecontext
• [x] Add caching to avoid duplicate recursion in heritage propagation
• [x] Changelog (this is a breaking change!)