feat: add NitroFetchRequest type and enhance $fetch's request type

[didavid61202]

Enhance the $fetch request's type by inferring the server route's string literal (InternalApi interface). supporting auto-complete and showing type hints.

🔗 Linked issue

resolves nuxt/framework#208

❓ 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

Add a new type NitroFetchRequest to Enhance $fetch's request type by inferring the generated server route's string literal (InternalApi interface).

This will provide better DX and prevent typos while $fetch by supporting auto-complete and showing type hints when entering the request. And should still be able to pass other valid request URLs like https://example.com/api or Request object like new Request('/api/test')

This will also provide Nuxt 3's useFetch and useLazyFetch to also have type hints on request parameters with little type changes. see issue nuxt/nuxt#13934 and PR nuxt/framework#4825

Usage scenario

// assume the project contains routes/api/test.ts
const result = await $fetch( /** IDE should show hint: '/api/test' */ )

const request: NitroFetchRequest = /** IDE should show hint: '/api/test' */

$fetch('/api/test') // ok
$fetch('https://example.com/api') // ok
$fetch(new Request('api/test')) // ok

// assume no routes/other.ts
$fetch('other') // type error: Argument of type '"other"' is not assignable to parameter of type 'FetchRequestUrl | Ref<FetchRequestUrl> | (() => FetchRequestUrl)'.

📝 Checklist

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

[danielroe]

I love it! ❤️

[pi0]

Thanks @didavid61202 @danielroe 💚