Turbopack: fix loading of externals on Edge (#72349)
- `__turbopack_external_require__("node:buffer")` becomes
`__turbopack_external_require__("node:buffer", () =>
require("node:buffer"))`.
- This way, running esbuild on the Turbopack output will correctly
detect usage of Node builtins and is able to polyfill them
- To make that `require` the global (non-shadowed) one, change the
previous `t: require` item from `__turbopack_context__` to `t:
__turbopack_require_real__` and the fake require added in
https://github.com/vercel/next.js/pull/70255 to
`__turbopack_stub_require_`
Closes PACK-3389
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Co-authored-by: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
