Support "equivalent to" for values

[danvk]

Fixes #167

Weirdly the Resolve helper only resolves types at the top level, not in functions:

interface Point {
  x: number;
  y: number;
}

type Resolve<Raw> = Raw extends Function ? Raw : { [K in keyof Raw]: Raw[K] };
function foo(pt: Point) {
  let k: keyof Point;
  for (k in pt) {
    // ^? let k: keyof Point
    type SynthK = Resolve<keyof Point>;
    //   ^? type SynthK = keyof Point
  }
}

type SynthT2 = Resolve<keyof Point>;
//   ^? type SynthT2 = "x" | "y"`);

This might be microsoft/TypeScript#49852