An enum describing what kind of type a given `__Type` is.
- SCALARIndicates this type is a scalar.
- OBJECTIndicates this type is an object. `fields` and `interfaces` are valid fields.
- INTERFACEIndicates this type is an interface. `fields`, `interfaces`, and `possibleTypes` are valid fields.
- UNIONIndicates this type is a union. `possibleTypes` is a valid field.
- ENUMIndicates this type is an enum. `enumValues` is a valid field.
- INPUT_OBJECTIndicates this type is an input object. `inputFields` is a valid field.
- LISTIndicates this type is a list. `ofType` is a valid field.
- NON_NULLIndicates this type is a non-null. `ofType` is a valid field.