Add `Route` and `LinkProps` stub generics (#54226)
Closes #53732. Closes #52929.
When using the statically typed routes feature, we might have code like:
```ts
export function Card<T extends string>({ href }: { href: Route<T> | URL })...
export function Card<T extends string>({ href }: LinkProps<T>)...
```
To statically check `<Card href={...}>` and make sure it's `href` is an existing route. However, in certain cases these route types are not generated (e.g. running `tsc` directly w/o a `next dev` or `next build`), which results in TS errors.
This PR adds stub generics to `Route` and `LinkProps` so even if that plugin isn't executed, these types will not block type checking.
