Union types are not applied on properties

I expect properties to inherit union types

```typescript
type Student = {
type: 'student'
}

type Teacher = {
type: 'teacher'
}

const getType = (someone : Student | Teacher) => someone.type;

const type = getType({ type: 'student' });

('student' : typeof type);
// ^ string literal `teacher` [1] is incompatible with string literal `student` [2].
```