[rn] enabled disableLegacyMode everywhere (#34947)

Stacked on #34946

This should be a noop, now that the legacy renderers are not being
sync'd.

DiffTrain build for [dd53a94](dd53a94)

Author: rickhanlonii

compiled-rn/VERSION_NATIVE_FB

@@ -1 +1 @@
-19.3.0-native-fb-90817f88-20251027
+19.3.0-native-fb-dd53a946-20251027

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<23f1b6bb3ad4f31d9d503b389ee2e4ff>>
+ * @generated SignedSource<<c017be7f331c9766262986fc7e8adc2d>>
  */
 
 "use strict";
@@ -126,10 +126,20 @@ __DEV__ &&
         throw Error("Target container is not a DOM element.");
       return createPortal$1(children, container, null, key);
     };
-    exports.flushSync = function () {
-      throw Error(
-        "Expected this build of React to not support legacy mode but it does. This is a bug in React."
-      );
+    exports.flushSync = function (fn) {
+      var previousTransition = ReactSharedInternals.T,
+        previousUpdatePriority = Internals.p;
+      try {
+        if (((ReactSharedInternals.T = null), (Internals.p = 2), fn))
+          return fn();
+      } finally {
+        (ReactSharedInternals.T = previousTransition),
+          (Internals.p = previousUpdatePriority),
+          Internals.d.f() &&
+            console.error(
+              "flushSync was called from inside a lifecycle method. React cannot flush when React is already rendering. Consider moving this call to a scheduler task or micro task."
+            );
+      }
     };
     exports.preconnect = function (href, options) {
       "string" === typeof href && href
@@ -404,5 +414,5 @@ __DEV__ &&
     exports.useFormStatus = function () {
       return resolveDispatcher().useHostTransitionStatus();
     };
-    exports.version = "19.3.0-native-fb-90817f88-20251027";
+    exports.version = "19.3.0-native-fb-dd53a946-20251027";
   })();

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-prod.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<4a87ccb0f35a6c88be76a74459be0cf7>>
+ * @generated SignedSource<<1360441d7f7b830ff98859fb60d0a18c>>
  */
 
 "use strict";
@@ -78,10 +78,16 @@ exports.createPortal = function (children, container) {
     throw Error(formatProdErrorMessage(299));
   return createPortal$1(children, container, null, key);
 };
-exports.flushSync = function () {
-  throw Error(
-    "Expected this build of React to not support legacy mode but it does. This is a bug in React."
-  );
+exports.flushSync = function (fn) {
+  var previousTransition = ReactSharedInternals.T,
+    previousUpdatePriority = Internals.p;
+  try {
+    if (((ReactSharedInternals.T = null), (Internals.p = 2), fn)) return fn();
+  } finally {
+    (ReactSharedInternals.T = previousTransition),
+      (Internals.p = previousUpdatePriority),
+      Internals.d.f();
+  }
 };
 exports.preconnect = function (href, options) {
   "string" === typeof href &&
@@ -203,4 +209,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactSharedInternals.H.useHostTransitionStatus();
 };
-exports.version = "19.3.0-native-fb-90817f88-20251027";
+exports.version = "19.3.0-native-fb-dd53a946-20251027";

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-profiling.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<4a87ccb0f35a6c88be76a74459be0cf7>>
+ * @generated SignedSource<<1360441d7f7b830ff98859fb60d0a18c>>
  */
 
 "use strict";
@@ -78,10 +78,16 @@ exports.createPortal = function (children, container) {
     throw Error(formatProdErrorMessage(299));
   return createPortal$1(children, container, null, key);
 };
-exports.flushSync = function () {
-  throw Error(
-    "Expected this build of React to not support legacy mode but it does. This is a bug in React."
-  );
+exports.flushSync = function (fn) {
+  var previousTransition = ReactSharedInternals.T,
+    previousUpdatePriority = Internals.p;
+  try {
+    if (((ReactSharedInternals.T = null), (Internals.p = 2), fn)) return fn();
+  } finally {
+    (ReactSharedInternals.T = previousTransition),
+      (Internals.p = previousUpdatePriority),
+      Internals.d.f();
+  }
 };
 exports.preconnect = function (href, options) {
   "string" === typeof href &&
@@ -203,4 +209,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactSharedInternals.H.useHostTransitionStatus();
 };
-exports.version = "19.3.0-native-fb-90817f88-20251027";
+exports.version = "19.3.0-native-fb-dd53a946-20251027";