[FB] disable legacy mode in modern build

Disables legacy mode in www-modern and removes the entrypoint hack in tests since we gate legacy mode tests now

Additionally disables test utils because this relies on legacy mode.

Additionally gates react-test-renderer test for unstable_Scope because it seems to also rely on legacy roots.

packages/react-dom/index.modern.fb.js

@@ -9,6 +9,8 @@
 
 export {default as __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED} from './src/ReactDOMSharedInternals';
 export {
+  createRoot,
+  hydrateRoot,
   createPortal,
   flushSync,
   unstable_batchedUpdates,
@@ -25,4 +27,4 @@ export {
   version,
 } from './src/client/ReactDOM';
 
-export {createRoot, hydrateRoot} from './src/client/ReactDOMRootFB';
+// export {createRoot, hydrateRoot} from './src/client/ReactDOMRootFB';

packages/react/index.modern.fb.js

@@ -33,6 +33,7 @@ export {
   unstable_Activity,
   unstable_Scope,
   unstable_SuspenseList,
+  unstable_TracingMarker,
   unstable_getCacheForType,
   unstable_useCacheRefresh,
   unstable_useMemoCache,
@@ -48,10 +49,10 @@ export {
   useLayoutEffect,
   useMemo,
   useOptimistic,
+  useSyncExternalStore,
   useReducer,
   useRef,
   useState,
-  useSyncExternalStore,
   useTransition,
   useActionState,
   version,

scripts/jest/setupHostConfigs.js

@@ -14,11 +14,6 @@ function resolveEntryFork(resolvedEntry, isFBBundle) {
   // .js
 
   if (isFBBundle) {
-    if (__EXPERIMENTAL__) {
-      // We can't currently use the true modern entry point because too many tests fail.
-      // TODO: Fix tests to not use ReactDOM.render or gate them. Then we can remove this.
-      return resolvedEntry;
-    }
     const resolvedFBEntry = resolvedEntry.replace(
       '.js',
       __EXPERIMENTAL__ ? '.modern.fb.js' : '.classic.fb.js'