performance: don't compile on hover on dev (#51830)
An annoying issue that slows down compilation times in dev for Next is
that we might trigger compilation of a page via hover on app.
We do this because we want the same experience in production and dev and
the prefetching is important for instantaneous loading states.
The alternative in this PR is that we don't prefetch at all anymore in
dev but instead, when we handle navigation, we can force a prefetch
navigation.
The slight compromise with this approach is that you can't test
prefetching anymore in dev.
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