improve dynamic reexporting (#5452)
### Description
This fixes some problems when `export * from "client component"`, as
`"use client"` creates a non-enumerable Proxy object, so we need to
really redirect property access.
* `__turbopack_export_namespace__` counts as dynamic
* use Proxy to correctly reexport non-enumerable or changing objects
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Co-authored-by: Alex Kirszenberg <alex.kirszenberg@vercel.com>
