feat(nuxt): add support for nuxt/kit subpath for local use

[danielroe]

🔗 Linked issue

resolves #12339

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 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

This adds a nuxt/kit import for using kit utilities without adding @nuxt/kit as a dependency. This is useful within your own project, such as within the auto-scanned ~/modules directory (#19394).

Note: module, layer or library authors should import from @nuxt/kit instead, which should be a dependency of their package.

📝 Checklist

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

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[pi0]

LGTM. Only how we can document it better in module guide?

[danielroe]

Good point. Linking @Atinux and @lihbr - they may well have a good idea about how to document in #18551.