Implement experimental_useOptimisticState (#26740)

This adds an experimental hook tentatively called useOptimisticState.
(The actual name needs some bikeshedding.)

The headline feature is that you can use it to implement optimistic
updates. If you set some optimistic state during a transition/action,
the state will be automatically reverted once the transition completes.

Another feature is that the optimistic updates will be continually
rebased on top of the latest state.

It's easiest to explain with examples; we'll publish documentation as
the API gets closer to stabilizing. See tests for now.

Technically the use cases for this hook are broader than just optimistic
updates; you could use it implement any sort of "pending" state, such as
the ones exposed by useTransition and useFormStatus. But we expect
people will most often reach for this hook to implement the optimistic
update pattern; simpler cases are covered by those other hooks.

DiffTrain build for [491aec5](491aec5)

Author: acdlite

compiled/facebook-www/REVISION

@@ -1 +1 @@
-9545e4810c2dc8922f575b6d8f726503a7345d0c
+491aec5d6113ce5bae7c10966bc38a4a8fc091a8

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

@@ -27,7 +27,7 @@ if (
 }
           "use strict";
 
-var ReactVersion = "18.3.0-www-classic-0ae2769a";
+var ReactVersion = "18.3.0-www-classic-9b9fa2f6";
 
 // ATTENTION
 // When adding new symbols to this file,
@@ -2026,6 +2026,11 @@ function useEffectEvent(callback) {
 
   return dispatcher.useEffectEvent(callback);
 }
+function useOptimisticState(passthrough, reducer) {
+  var dispatcher = resolveDispatcher(); // $FlowFixMe[not-a-function] This is unstable, thus optional
+
+  return dispatcher.useOptimisticState(passthrough, reducer);
+}
 
 // Helpers to patch console.logs to avoid logging during side-effect free
 // replaying on render function. This currently only patches the object
@@ -4175,6 +4180,7 @@ exports.createMutableSource = createMutableSource;
 exports.createRef = createRef;
 exports.createServerContext = createServerContext;
 exports.experimental_useEffectEvent = useEffectEvent;
+exports.experimental_useOptimisticState = useOptimisticState;
 exports.forwardRef = forwardRef;
 exports.isValidElement = isValidElement$1;
 exports.jsx = jsx;

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

@@ -27,7 +27,7 @@ if (
 }
           "use strict";
 
-var ReactVersion = "18.3.0-www-modern-3898c4ac";
+var ReactVersion = "18.3.0-www-modern-32c95640";
 
 // ATTENTION
 // When adding new symbols to this file,
@@ -2026,6 +2026,11 @@ function useEffectEvent(callback) {
 
   return dispatcher.useEffectEvent(callback);
 }
+function useOptimisticState(passthrough, reducer) {
+  var dispatcher = resolveDispatcher(); // $FlowFixMe[not-a-function] This is unstable, thus optional
+
+  return dispatcher.useOptimisticState(passthrough, reducer);
+}
 
 // Helpers to patch console.logs to avoid logging during side-effect free
 // replaying on render function. This currently only patches the object
@@ -4139,6 +4144,7 @@ exports.createMutableSource = createMutableSource;
 exports.createRef = createRef;
 exports.createServerContext = createServerContext;
 exports.experimental_useEffectEvent = useEffectEvent;
+exports.experimental_useOptimisticState = useOptimisticState;
 exports.forwardRef = forwardRef;
 exports.isValidElement = isValidElement$1;
 exports.jsx = jsx;

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

@@ -536,6 +536,12 @@ exports.createServerContext = function (globalName, defaultValue) {
 exports.experimental_useEffectEvent = function (callback) {
   return ReactCurrentDispatcher.current.useEffectEvent(callback);
 };
+exports.experimental_useOptimisticState = function (passthrough, reducer) {
+  return ReactCurrentDispatcher.current.useOptimisticState(
+    passthrough,
+    reducer
+  );
+};
 exports.forwardRef = function (render) {
   return { $$typeof: REACT_FORWARD_REF_TYPE, render: render };
 };
@@ -646,4 +652,4 @@ exports.useSyncExternalStore = function (
   );
 };
 exports.useTransition = useTransition;
-exports.version = "18.3.0-www-classic-993671e7";
+exports.version = "18.3.0-www-classic-f9e05cb4";

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

@@ -529,6 +529,12 @@ exports.createServerContext = function (globalName, defaultValue) {
 exports.experimental_useEffectEvent = function (callback) {
   return ReactCurrentDispatcher.current.useEffectEvent(callback);
 };
+exports.experimental_useOptimisticState = function (passthrough, reducer) {
+  return ReactCurrentDispatcher.current.useOptimisticState(
+    passthrough,
+    reducer
+  );
+};
 exports.forwardRef = function (render) {
   return { $$typeof: REACT_FORWARD_REF_TYPE, render: render };
 };
@@ -638,4 +644,4 @@ exports.useSyncExternalStore = function (
   );
 };
 exports.useTransition = useTransition;
-exports.version = "18.3.0-www-modern-d633a116";
+exports.version = "18.3.0-www-modern-2e6e6832";

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

@@ -547,6 +547,12 @@ exports.createServerContext = function (globalName, defaultValue) {
 exports.experimental_useEffectEvent = function (callback) {
   return ReactCurrentDispatcher.current.useEffectEvent(callback);
 };
+exports.experimental_useOptimisticState = function (passthrough, reducer) {
+  return ReactCurrentDispatcher.current.useOptimisticState(
+    passthrough,
+    reducer
+  );
+};
 exports.forwardRef = function (render) {
   return { $$typeof: REACT_FORWARD_REF_TYPE, render: render };
 };
@@ -657,7 +663,7 @@ exports.useSyncExternalStore = function (
   );
 };
 exports.useTransition = useTransition;
-exports.version = "18.3.0-www-classic-1306d154";
+exports.version = "18.3.0-www-classic-8122ba25";
 
           /* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
 if (

compiled/facebook-www/React-profiling.modern.js

@@ -540,6 +540,12 @@ exports.createServerContext = function (globalName, defaultValue) {
 exports.experimental_useEffectEvent = function (callback) {
   return ReactCurrentDispatcher.current.useEffectEvent(callback);
 };
+exports.experimental_useOptimisticState = function (passthrough, reducer) {
+  return ReactCurrentDispatcher.current.useOptimisticState(
+    passthrough,
+    reducer
+  );
+};
 exports.forwardRef = function (render) {
   return { $$typeof: REACT_FORWARD_REF_TYPE, render: render };
 };
@@ -649,7 +655,7 @@ exports.useSyncExternalStore = function (
   );
 };
 exports.useTransition = useTransition;
-exports.version = "18.3.0-www-modern-01657d31";
+exports.version = "18.3.0-www-modern-eff148b0";
 
           /* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
 if (