fix(edge): allow Request cloning via NextRequest (vercel#53157)

### What?

Allow the following:

```ts
new NextRequest(new Request(...))
```

### Why?

Cloning a request by passing it to the constructor of another `Request` is allowed by the spec: https://developer.mozilla.org/en-US/docs/Web/API/Request/Request#parameters

### How?

If the passed argument is an instance of `Request`, we pass it as-is to `super()`

Fixes vercel#52967
Closes NEXT-1468

packages/next/src/server/web/spec-extension/request.ts

@@ -20,7 +20,8 @@ export class NextRequest extends Request {
     const url =
       typeof input !== 'string' && 'url' in input ? input.url : String(input)
     validateURL(url)
-    super(url, init)
+    if (input instanceof Request) super(input)
+    else super(url, init)
     const nextUrl = new NextURL(url, {
       headers: toNodeOutgoingHttpHeaders(this.headers),
       nextConfig: init.nextConfig,

test/unit/web-runtime/next-request.test.ts

@@ -21,3 +21,15 @@ it('should allow the 2nd parameter to be undefined', () => {
     '/'
   )
 })
+
+it('should clone Request with headers', () => {
+  const request = new Request('https://example.com', {
+    headers: { 'x-foo': 'bar' },
+  })
+
+  const nextRequest = new NextRequest(request)
+
+  expect(Object.fromEntries(nextRequest.headers)).toEqual(
+    Object.fromEntries(request.headers)
+  )
+})