Enable enableUnifiedSyncLane (#27646)

<!--
  Thanks for submitting a pull request!
We appreciate you spending the time to work on these changes. Please
provide enough information so that others can review your pull request.
The three fields below are mandatory.

Before submitting a pull request, please make sure the following is
done:

1. Fork [the repository](https://github.com/facebook/react) and create
your branch from `main`.
  2. Run `yarn` in the repository root.
3. If you've fixed a bug or added code that should be tested, add tests!
4. Ensure the test suite passes (`yarn test`). Tip: `yarn test --watch
TestName` is helpful in development.
5. Run `yarn test --prod` to test in the production environment. It
supports the same options as `yarn test`.
6. If you need a debugger, run `yarn test --debug --watch TestName`,
open `chrome://inspect`, and press "Inspect".
7. Format your code with
[prettier](https://github.com/prettier/prettier) (`yarn prettier`).
8. Make sure your code lints (`yarn lint`). Tip: `yarn linc` to only
check changed files.
  9. Run the [Flow](https://flowtype.org/) type checks (`yarn flow`).
  10. If you haven't already, complete the CLA.

Learn more about contributing:
https://reactjs.org/docs/how-to-contribute.html
-->

## Summary

<!--
Explain the **motivation** for making this change. What existing problem
does the pull request solve?
-->
The flag has been tested internally on WWW, should be good to set to
true for OSS. Added a dynamic flag for fb RN.

## How did you test this change?

<!--
Demonstrate the code is solid. Example: The exact commands you ran and
their output, screenshots / videos if the pull request changes the user
interface.
How exactly did you verify that your PR solves the issue you wanted to
solve?
  If you leave this empty, your PR will very likely be closed.
-->
yarn test

DiffTrain build for [52d542a](52d542a)

Author: tyao1

compiled/facebook-www/REVISION

@@ -1 +1 @@
-2c8a139a593e0294c3a6953d74b451bd05fdcfca
+52d542ad6d410008c495084f511247f43387055f

compiled/facebook-www/React-prod.classic.js

@@ -587,4 +587,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactCurrentDispatcher.current.useTransition();
 };
-exports.version = "18.3.0-www-classic-4b8ff8ef";
+exports.version = "18.3.0-www-classic-4602af1b";

compiled/facebook-www/ReactTestRenderer-dev.classic.js

@@ -1180,7 +1180,7 @@ if (__DEV__) {
     var DefaultLane =
       /*                     */
       32;
-    var SyncUpdateLanes = SyncLane;
+    var SyncUpdateLanes = SyncLane | InputContinuousLane | DefaultLane;
     var TransitionHydrationLane =
       /*                */
       64;
@@ -1275,6 +1275,14 @@ if (__DEV__) {
     var nextRetryLane = RetryLane1;
 
     function getHighestPriorityLanes(lanes) {
+      {
+        var pendingSyncLanes = lanes & SyncUpdateLanes;
+
+        if (pendingSyncLanes !== 0) {
+          return pendingSyncLanes;
+        }
+      }
+
       switch (getHighestPriorityLane(lanes)) {
         case SyncHydrationLane:
           return SyncHydrationLane;
@@ -1873,7 +1881,9 @@ if (__DEV__) {
       var renderLane = getHighestPriorityLane(renderLanes);
       var lane;
 
-      {
+      if ((renderLane & SyncUpdateLanes) !== NoLane) {
+        lane = SyncHydrationLane;
+      } else {
         switch (renderLane) {
           case SyncLane:
             lane = SyncHydrationLane;
@@ -25720,7 +25730,7 @@ if (__DEV__) {
       return root;
     }
 
-    var ReactVersion = "18.3.0-www-classic-4b8ff8ef";
+    var ReactVersion = "18.3.0-www-classic-4602af1b";
 
     // Might add PROFILE later.
 

compiled/facebook-www/ReactTestRenderer-dev.modern.js

@@ -1180,7 +1180,7 @@ if (__DEV__) {
     var DefaultLane =
       /*                     */
       32;
-    var SyncUpdateLanes = SyncLane;
+    var SyncUpdateLanes = SyncLane | InputContinuousLane | DefaultLane;
     var TransitionHydrationLane =
       /*                */
       64;
@@ -1275,6 +1275,14 @@ if (__DEV__) {
     var nextRetryLane = RetryLane1;
 
     function getHighestPriorityLanes(lanes) {
+      {
+        var pendingSyncLanes = lanes & SyncUpdateLanes;
+
+        if (pendingSyncLanes !== 0) {
+          return pendingSyncLanes;
+        }
+      }
+
       switch (getHighestPriorityLane(lanes)) {
         case SyncHydrationLane:
           return SyncHydrationLane;
@@ -1873,7 +1881,9 @@ if (__DEV__) {
       var renderLane = getHighestPriorityLane(renderLanes);
       var lane;
 
-      {
+      if ((renderLane & SyncUpdateLanes) !== NoLane) {
+        lane = SyncHydrationLane;
+      } else {
         switch (renderLane) {
           case SyncLane:
             lane = SyncHydrationLane;
@@ -25720,7 +25730,7 @@ if (__DEV__) {
       return root;
     }
 
-    var ReactVersion = "18.3.0-www-modern-aa96362d";
+    var ReactVersion = "18.3.0-www-modern-9a10673b";
 
     // Might add PROFILE later.