fix(webpack,rspack): incorrect assumption about the current working directory in webpack and rspack

[NullVoxPopuli]

🔗 Linked issue

#375

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Build tools can decide to resolve from wherever they want, and it's not guaranteed that the place they resolve from is the user's current working directory.

For example this reproduction of the failure case where in embroider (which uses a node_modules/.embroider/ directory for the root -- and I imagine svelte apps, too with their .svelte directory)
embroider-build/embroider#1843
Repro here: https://github.com/NullVoxPopuli/embroider-3--unplugin-plugin-loads-app-files

Here is a patched version of unplugin which allows the build to succeed: NullVoxPopuli/embroider-3--unplugin-plugin-loads-app-files#1

📝 Checklist

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