Throw when generateStaticParams returns invalid values (#95968)
> [!TIP]
> This PR is best reviewed commit by commit.
### Why?
`generateStaticParams` must return an array of objects, but Next.js does
not currently provide a clear error when it returns something else.
### How?
- Throw when `generateStaticParams` does not return an array.
- Throw when an item in the returned array is not an object.
- Keep allowing `{}`. The follow-up rejects it with `output: 'export'`
when it leaves a dynamic route parameter missing.
Follow-up: #95969
Supersedes #95388.
<!-- NEXT_JS_LLM -->
Co-authored-by: SukkaW <isukkaw@gmail.com>
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Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
