fix!: injection fields completion for nuxt app instance and page meta

[kazupon]

🔗 Linked issue

resolves #1704

❓ 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)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR is to ensure that interpolation for fields injected into the nuxt app also works for injections by Nuxt and the user's plugins provided.

The old way was to generate the type in the Nuxt template dynamically, but that way overwrites the existing type, which was as described in #1704.

This PR is for the same issue, although PageMeta's type generation also involves a destructive change.
It's fixed to nuxtI18n only, but that key rarely conflicts with user-defined keys in PageMeta.

📝 Checklist

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

[kazupon]

This is WIP