fix(rsc): fix internal import to allow stable react vendor chunk (#824)

Just curiosity. I was wondering what would be a Vite equivalent of https://github.com/web-infra-dev/rsbuild/blob/main/packages/plugin-react/src/splitChunks.ts

Testing `manualChunks` is postponed for #940 for now since that's going to be tricky for rolldown-vite ci.

Author: hi-ogawa

packages/rsc/src/plugin.ts

@@ -737,7 +737,7 @@ function vitePluginUseServer(): Plugin[] {
           serverReferences[normalizedId] = id;
           const name = this.environment.name === "client" ? "browser" : "ssr";
           output.prepend(
-            `import * as $$ReactClient from "${PKG_NAME}/${name}";\n`,
+            `import * as $$ReactClient from "${PKG_NAME}/react/${name}";\n`,
           );
           return {
             code: output.toString(),