Export return type for GetStaticPaths (#16580)

* feat Export return type for GetStaticPaths

* add Duplicate generic

Co-authored-by: Luis Alvarez D <luis@vercel.com>

Author: arthurjdam

packages/next/types/index.d.ts

@@ -96,12 +96,14 @@ export type InferGetStaticPropsType<T> = T extends GetStaticProps<infer P, any>
   ? P
   : never
 
-export type GetStaticPaths<
-  P extends ParsedUrlQuery = ParsedUrlQuery
-> = () => Promise<{
+export type GetStaticPathsResult<P extends ParsedUrlQuery = ParsedUrlQuery> = {
   paths: Array<string | { params: P }>
   fallback: boolean | 'unstable_blocking'
-}>
+}
+
+export type GetStaticPaths<
+  P extends ParsedUrlQuery = ParsedUrlQuery
+> = () => Promise<GetStaticPathsResult<P>>
 
 export type GetServerSidePropsContext<
   Q extends ParsedUrlQuery = ParsedUrlQuery