Add support for catchall with new router (#38439)

Adds support for `[...slug]` dynamic segments.

I found there's an inconsistency in query/params providing and added a quick fix for it now. Will update the handling in a follow-up PR to ensure it's consistently providing dynamic params outside of `query`.

Follow-up of #37551 and #38415.


## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)

packages/next/server/app-render.tsx

@@ -385,15 +385,24 @@ export async function renderToHTML(
     // TODO: use correct matching for dynamic routes to get segment param
     const segmentParam =
       segment.startsWith('[') && segment.endsWith(']')
-        ? segment.slice(1, -1)
+        ? segment.slice(segment.startsWith('[...') ? 4 : 1, -1)
         : null
 
-    if (!segmentParam || !pathParams[segmentParam]) {
+    if (!segmentParam || (!pathParams[segmentParam] && !query[segmentParam])) {
       return null
     }
 
-    // @ts-expect-error TODO:  handle case where value is an array
-    return { param: segmentParam, value: pathParams[segmentParam] }
+    return {
+      param: segmentParam,
+      // @ts-expect-error TODO:  handle case where value is an array
+      value:
+        // TODO: this should only read from `pathParams`. There's an inconsistency where `query` holds params currently which has to be fixed.
+        pathParams[segmentParam] ??
+        (Array.isArray(query[segmentParam])
+          ? // @ts-expect-error TODO:  handle case where value is an array
+            query[segmentParam].join('/')
+          : query[segmentParam]),
+    }
   }
 
   const createFlightRouterStateFromLoaderTree = ([
@@ -546,10 +555,9 @@ export async function renderToHTML(
         | GetServerSidePropsContext
         | getServerSidePropsContextPage = {
         headers,
-        // TODO: convert to NextCookies
         cookies,
         layoutSegments: segmentPath,
-        // TODO: change this to be URLSearchParams instead?
+        // TODO: Currently query holds params and pathname is not the actual pathname, it holds the dynamic parameter
         ...(isPage ? { query, pathname } : {}),
         ...(pageIsDynamic ? { params: currentParams } : undefined),
         ...(isPreview