Improve client boundary source type detection (#47532)Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>
Currently in a client boundary file, we only explicitly export
individual fields in ESM (`export foo`) when the source type is
`module`. However in most of the time SWC gives the `auto` source type.
This PR improves the type detection a bit so if it's `auto` and we do
see ESM exports collected, we assume it's ESM and re-export these
fields.
Fixes #41940, fix NEXT-796
([link](https://linear.app/vercel/issue/NEXT-796)).
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Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>