UnionToIntersection

Given a union type U = T1 | T2 | ..., returns an intersected type (T1 & T2 & ...).

Uses distributive conditional types and inference from conditional types. This works because multiple candidates for the same type variable in contra-variant positions causes an intersection type to be inferred. https://www.typescriptlang.org/docs/handbook/advanced-types.html#type-inference-in-conditional-types https://stackoverflow.com/questions/50374908/transform-union-type-to-intersection-type