57. implement ObjectPaths<O>

Implement ObjectPaths<O> to return all valid paths to properties.

type Obj = {
  a: {
    b: {
      c: 1,
      d: 2
    },
    e: 1
  },
  f: 3
}

type A = ObjectPaths<Obj>
// 'a.b.c' | 'a.b.d' | 'a.e' | 'f'