[turbopack] Lazily compile dynamic imports in development (client side) (#97203)
## Summary
Defer compiling client-side dynamic import targets in Turbopack
development until the browser requests their manifest chunk. This avoids
compiling untouched dynamic imports while preserving server-side
imports, CSS loading, Server Actions, source maps, and Fast Refresh
behavior.
One caveat on this is next/dynamic still does some eagerness. I looked a
bit at changing things. But it breaks some of the guarantees there and
decided to leave it off the table.
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Co-authored-by: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>