Update internal Flow type

Updates our internal Flow type for useFormState to allow for synchronous
actions. I tried to make it match what the TypeScript equivalent would
be, so although Flow does not include an Awaited type helper, I copied
the one from TypeScript and added it to our internal types.

Unfortunately this led to a few "Recursion limit exceeded" Flow errors
in the Fiber implementation. I wasn't able to figure out whether these
were legit type errors, or if the types were correct but the
recursiveness of the types tripped some internal limit. But since this
only affects the type coverage of our internal implementation and not
the public API, I sprinkled in some `any`s and called it a day.

packages/react-dom-bindings/src/shared/ReactDOMFormActions.js

@@ -8,6 +8,7 @@
  */
 
 import type {Dispatcher} from 'react-reconciler/src/ReactInternalTypes';
+import type {Awaited} from 'shared/ReactTypes';
 
 import {enableAsyncActions, enableFormActions} from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
@@ -76,10 +77,10 @@ export function useFormStatus(): FormStatus {
 }
 
 export function useFormState<S, P>(
-  action: (S, P) => Promise<S>,
-  initialState: S,
+  action: (Awaited<S>, P) => S,
+  initialState: Awaited<S>,
   permalink?: string,
-): [S, (P) => void] {
+): [Awaited<S>, (P) => void] {
   if (!(enableFormActions && enableAsyncActions)) {
     throw new Error('Not implemented.');
   } else {

packages/react-dom/index.experimental.js

@@ -31,6 +31,7 @@ export {
   version,
 } from './src/client/ReactDOM';
 
+import type {Awaited} from 'shared/ReactTypes';
 import type {FormStatus} from 'react-dom-bindings/src/shared/ReactDOMFormActions';
 import {useFormStatus, useFormState} from './src/client/ReactDOM';
 
@@ -45,10 +46,10 @@ export function experimental_useFormStatus(): FormStatus {
 }
 
 export function experimental_useFormState<S, P>(
-  action: (S, P) => Promise<S>,
-  initialState: S,
+  action: (Awaited<S>, P) => S,
+  initialState: Awaited<S>,
   permalink?: string,
-): [S, (P) => void] {
+): [Awaited<S>, (P) => void] {
   if (__DEV__) {
     console.error(
       'useFormState is now in canary. Remove the experimental_ prefix. ' +

packages/react-dom/server-rendering-stub.js

@@ -34,6 +34,7 @@ import {
   useFormStatus,
   useFormState,
 } from './src/server/ReactDOMServerRenderingStub';
+import type {Awaited} from 'shared/ReactTypes';
 
 export function experimental_useFormStatus(): FormStatus {
   if (__DEV__) {
@@ -46,10 +47,10 @@ export function experimental_useFormStatus(): FormStatus {
 }
 
 export function experimental_useFormState<S, P>(
-  action: (S, P) => Promise<S>,
-  initialState: S,
+  action: (Awaited<S>, P) => S,
+  initialState: Awaited<S>,
   permalink?: string,
-): [S, (P) => void] {
+): [Awaited<S>, (P) => void] {
   if (__DEV__) {
     console.error(
       'useFormState is now in canary. Remove the experimental_ prefix. ' +