remove HMR polling in favor of more targeted events (#54406)
This removes the client-side polling logic that we're doing on every HMR
tick in favor of events like `addedPage` / `removedPage`. It was leading
to a lot of misc issues & confusion surrounding error/404 pages being
polled needlessly.
Instead this updates `addedPage` / `removedPage` to be emitted on the
server, so that we can leverage those hooks to reload when necessary.
Fixes #10024
Fixes #51132
Closes NEXT-1372
related discussion: https://github.com/vercel/next.js/discussions/40000
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