This is crucial especially for generated Angular wrappers. Previously,
if we had a property like

```ts
@Property({ type: String, reflect: true })
public placement: 'top' | 'bottom' = 'top';
```

the analyzer would widen its type to `string`. Then, the Angular
wrapper generator would emit

```ts
@input()
set placement(v: string) {
  this._ngZone.runOutsideAngular(() => (this._el.placement = v));
}
```

which fails type checking:

```
error TS2322: Type 'string' is not assignable to type '"top" | "bottom"'.
```