Clean up enableEagerAlternateStateNodeCleanup

Summary:
The `enableEagerAlternateStateNodeCleanup` flag is no longer read by the renderer, so the feature-flag definition and the two prelude overrides that forced it on become dead code. Drop the flag entry from `ReactNativeInternalFeatureFlags` (incl. its test mirror and the Fantom mock) and remove the `= true` assignments from the Airwave and FB4TV preludes. The dedicated `VirtualView-enableEagerAlternateStateNodeCleanup-itest.js` is folded into `VirtualView-itest.js`'s `memory management` describe so the shadow-node retention regression test continues to run, just no longer keyed on a non-existent flag.

Vendored React (`react-devtools-facade`), the append-only mobileconfig stable_id, and the generated `react-devtools-core` bundles are intentionally untouched.

Changelog:
[Internal]

Differential Revision: D110043719

Author: javache

packages/react-native/src/private/components/virtualview/__tests__/VirtualView-enableEagerAlternateStateNodeCleanup-itest.js

@@ -15,6 +15,7 @@ import type {NativeModeChangeEvent} from '../VirtualViewNativeComponent';
 
 import ensureInstance from '../../../__tests__/utilities/ensureInstance';
 import isUnreachable from '../../../__tests__/utilities/isUnreachable';
+import {createShadowNodeReferenceCountingRef} from '../../../__tests__/utilities/ShadowNodeReferenceCounter';
 import {getNodeFromPublicInstance} from '../../../../../Libraries/ReactPrivate/ReactNativePrivateInterface';
 import ReactNativeElement from '../../../webapis/dom/nodes/ReactNativeElement';
 import VirtualView, {_logs, VirtualViewMode} from '../VirtualView';
@@ -291,6 +292,28 @@ describe('memory management', () => {
 
     expect(isUnreachable(nullthrows(weakRef))).toBe(true);
   });
+
+  test('does not retain shadow node after becoming hidden', () => {
+    const root = Fantom.createRoot();
+
+    const [getReferenceCount, childRef] =
+      createShadowNodeReferenceCountingRef();
+    const viewRef = createRef<React.RefOf<VirtualView>>();
+
+    Fantom.runTask(() => {
+      root.render(
+        <VirtualView ref={viewRef}>
+          <Text ref={childRef}>Child</Text>
+        </VirtualView>,
+      );
+    });
+
+    expect(getReferenceCount()).toBeGreaterThan(0);
+
+    dispatchModeChangeEvent(viewRef.current, VirtualViewMode.Hidden);
+
+    expect(getReferenceCount()).toBe(0);
+  });
 });
 
 /**

packages/react-native/src/private/components/virtualview/__tests__/VirtualView-itest.js

@@ -9,12 +9,6 @@
  */
 
 module.exports = {
-  // When enableEagerAlternateStateNodeCleanup is enabled, alternate.stateNode is proactively
-  // pointed towards finishedWork's stateNode, releasing resources sooner.
-  // With enableEagerAlternateStateNodeCleanup enabled, we can remove workarounds in tests
-  // and have predictable memory model.
-  // See https://github.com/facebook/react/pull/33161 for details.
-  enableEagerAlternateStateNodeCleanup: true,
   enableFragmentRefs: true,
   enableFragmentRefsInstanceHandles: true,
   enableFragmentRefsTextNodes: true,