Export __COMPILER_RUNTIME in stable (#31540)

In order to make use of the compiler in stable releases (eg React 19 RC,
canary), we need to export the compiler runtime in the stable channel as
well.

packages/react/index.stable.js

@@ -9,6 +9,7 @@
 
 export {
   __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  __COMPILER_RUNTIME,
   act,
   Children,
   Component,