fix(nuxt): load payload after middleware and once final route is resolved

[danielroe]

🔗 Linked issue

nuxt/nuxt#14927

❓ 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 is not an alternative to #7567, but a separate fix. It ensures the data is only applied immediately before the route resolves (so after all middleware have been processed - and not when the data is prefetched)....

Where same asyncData keys are used for different routes (e.g. in a [slug].vue), this will resolve the issue, with one exception: if there are still additional async setups required and the keys collide.

In some ways this mitigates nuxt/nuxt#14927 because data isn't overwritten when it is prefetched, but only when the route is changed.

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Note: although it hotfixes content + prerender, we still would want to change content implementation as suspense doesn't work when swapping data out like this; instead, we want a route-based composable so that we can have two 'trees'. (useState doesn't work best when holding route-based data because it isn't naturally associated with a route... See nuxt/nuxt#14924.)

📝 Checklist

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

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