feat: support loading files from npm packages

[markbrockhoff]

🔗 Linked issue

Related: #2999

❓ Type of change

• [x] 📖 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)
• [x] ✨ 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

As proposed in #2999, I created a basic implementation for loading translation files form npm packages. This gives more flexibility in reusing and distributing translations. The feature should be especially useful for module / library authors wanting to provide translations which can be used to integrate with @nuxtjs/i18n.

📝 Checklist

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