Fix server component render condition (#35663)

We are currently using `!!ComponentMod.__next_rsc__` as the hint for the renderer to tell if the component is a server component, however that export field (`__next_rsc__`) is assigned to client components (`.client.[ext]`) as well. 

This PR adds a new `__next_rsc_server__` field which is only true when the component is a server component so the renderer can handle client components correctly.

## 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 `yarn lint`

packages/next/build/webpack/loaders/next-flight-server-loader.ts

@@ -186,6 +186,7 @@ export default async function transformSource(
       __webpack_require__,
       _: () => {\n${imports}\n}
     }`,
+    __next_rsc_server__: isServerComponent(resourcePath) ? 'true' : 'false',
   }
 
   if (isClientCompilation) {

packages/next/server/render.tsx

@@ -469,9 +469,9 @@ export async function renderToHTML(
 
   // We don't need to opt-into the flight inlining logic if the page isn't a RSC.
   const isServerComponent =
-    !!serverComponentManifest &&
     hasConcurrentFeatures &&
-    !!ComponentMod.__next_rsc__
+    !!serverComponentManifest &&
+    !!ComponentMod.__next_rsc_server__
 
   let Component: React.ComponentType<{}> | ((props: any) => JSX.Element) =
     renderOpts.Component