feat(vite): introduce vite:configResolved hook

[antfu]

🔗 Linked issue

danielroe/nuxt-vitest#130

#19968

❓ 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

For vite:extendConfig is intended to have the module modify the config, while in cases like nuxt-vitest, we want to retrieve the final configure passing to the Vite.

📝 Checklist

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

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[danielroe]

It might be worth doing the same for webpack.