fix: narrow legacy or composition vue-i18n types

[BobbieGoede]

🔗 Linked issue

• Incorrect types in the global $i18n object #3329
• types: locale property from nuxtApp.$i18n is string & computedRef<string> #2157

❓ 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 also prepares the types for the additional narrowing possible with intlify/vue-i18n#2094 in vue-i18n v11 and up.

Not sure if these changes https://github.com/nuxt-modules/i18n/pull/3341/files#diff-6651fe35cf71a075f9059641cd99a6d6a927b2cb77ab2a0b494eacf46735fe52R64-R70 are correct. It unwraps the extended property refs, but I'm not sure if these are the appropriate instances that need the unwrapped properties to match legacy and global component property types.

📝 Checklist

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