Closes [#66650](https://github.com/vercel/next.js/issues/66650)
Closes NEXT-3520
### What?
- Make Link not throw during prefetch if it received an invalid `href`
(see [#66650](https://github.com/vercel/next.js/issues/66650))
- Throw in dev mode if an invalid link was passed to `router.prefetch`
-- this matches current prod behavior
- (previously, we'd immediately exit out of `router.prefetch`, so the
user would see no indication that this'd fail in prod)
### Why?
If an invalid URL was passed to `<Link>`, the whole app would crash and
show "A client-side exception occurred". A failed prefetch should not
bring down the whole app.
Note that This preserves the current behavior of explicit
`router.prefetch(url)` throwing an error if `url` is invalid. We may
want to adjust this in the future, but that could be considered a
breaking change, so I'm leaving it out for now. This only affects
`Link`, which was intended to catch any errors thrown from
`router.prefetch`, but that bit was accidentally broken.
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