feat: configurable directory restructure

[BobbieGoede]

🔗 Linked issue

• [BUG?]: Locale resolver scans srcDir instead of rootDir #2983

❓ 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

This is still a work in progress!

This changes the way files are resolved and can be enabled by setting restructureDir: 'i18n'. This is no longer a breaking change as it is disabled by default allowing users a path to migrate before updating to v9, we will have to make sure to set the default values for v9 before release!

With restructureDir set to i18n the directory structure would look like so:

app/
server/
i18n/
  locales/
    en.json
    ja.json
  i18n.config.ts
  localeDetector.ts
nuxt.config.ts

And langDir will have a default value of locales, perhaps we may want to rename this to messages instead?

This kind of tackles #2983, as with this feature enabled we would resolve from <rootDir>/i18n/ for all i18n files.

📝 Checklist

• I have linked an issue or discussion.
• I have added tests (if possible).
• I have updated the documentation accordingly.

[kazupon]

Thanks!
Great works!
This looks good to me because this PR supports Nuxt4 and i18n-specific directories.

It might be good to be able to change the top directory name, as this might cause conflicts with users and 3rd vendors. restructure may accept string instead of boolean.
The option name restructureDir might be better.

[BobbieGoede]

@kazupon
Thanks for the feedback! I have changed the option to restructureDir which accepts a string so users can configure the directory themselves.

We should set the default value in a separate PR as that would be a breaking change, but these changes should be fully compatible with v8, so users can opt into the restructure.

I've tried to update the v9 docs to already reflect the new default values, hopefully I haven't missed anything 😅

[kazupon]

Well done!
Thank you so much always 💚 !