Add Route and LinkProps stub generics

[shuding]

Closes #53732. Closes #52929.

When using the statically typed routes feature, we might have code like:

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.