[next] fix re-mapping logic for index prefetches (#10750)

Follow-up to https://github.com/vercel/vercel/pull/10734 -- but considers that the static prefetch associated with `/` might be inside of a dir such as `index/index.prefetch.rsc`. 

To avoid any future matching conflicts, this PR updates to prefix all static prefetches

packages/next/src/utils.ts

@@ -3120,3 +3120,16 @@ export async function getServerlessPages(params: {
 
   return { pages, appPaths: normalizedAppPaths };
 }
+
+// to avoid any conflict with route matching/resolving, we prefix all prefetches (ie, __index.prefetch.rsc)
+// this is to ensure that prefetches are never matched for things like a greedy match on `index.{ext}`
+export function normalizePrefetches(prefetches: Record<string, FileFsRef>) {
+  const updatedPrefetches: Record<string, FileFsRef> = {};
+
+  for (const key in prefetches) {
+    const newKey = key.replace(/([^/]+\.prefetch\.rsc)$/, '__$1');
+    updatedPrefetches[newKey] = prefetches[key];
+  }
+
+  return updatedPrefetches;
+}