feat(nuxt): warn on external webpack/nitro/postcss config

[Lehoczky]

🔗 Linked issue

Well not an issue, but: https://youtu.be/a2r8Zr1hnEw?t=4166

I can create an issue too though:D

❓ 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

The main change is that with this PR, we check whether the user has a webpack.config, postcss.config, nitro.config file and not just a vite.config file.

For better performance, this check runs parallel to the bundling process, see this line.

One caveat is that regardless of whether the user has chosen webpack or vite as a builder, we will always look for both of their config files (for example a warning will be made about an existing webpack config file, even if the user uses vite). I thought this is a pretty unlikely scenario, but if needed, I can adjust the code to take into consideration the used builder as well. It wouldn't be such a big change.

As a small additional improvement, the loadBuilder() function is now more type safe, and gracefully handles when a builder cannot be resolved:

Before:

After:

📝 Checklist

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

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[danielroe]

This is nice 👌