feat: resolve actual subpaths before guessing

[danielroe]

🔗 Linked issue

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [x] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This resolves actual subpaths rather than guessing, so (for example) node-fetch-native/dist/polyfill.mjs can correctly be resolved to node-fetch-native/polyfill and back again.

📝 Checklist

• [x] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.

[codecov[bot]]

Codecov Report

Merging #527 (ee6ea64) into main (2049def) will decrease coverage by 0.33%. The diff coverage is 55.88%.

@@            Coverage Diff             @@
##             main     #527      +/-   ##
==========================================
- Coverage   63.96%   63.62%   -0.34%     
==========================================
  Files          55       55              
  Lines        3644     3665      +21     
  Branches      400      406       +6     
==========================================
+ Hits         2331     2332       +1     
- Misses       1299     1317      +18     
- Partials       14       16       +2     

Impacted Files	Coverage Δ
src/rollup/plugins/externals.ts	82.22% <55.88%> (-6.12%)	:arrow_down:

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[danielroe]

If you like this approach we can also extract into a mlly util.

[pi0]

A refactor to mlly would be nice idea for reverse resolving subpaths 👍🏼

[danielroe]

extracted:

• [ ] https://github.com/unjs/pkg-types/pull/47
• [ ] https://github.com/unjs/mlly/pull/89