[react] Add types for experimental_use

- [`experimental` entrypoint](https://unpkg.com/browse/react@0.0.0-experimental-c28f313e6-20220908/cjs/react.development.js)
- [implementation in `experimental`](https://unpkg.com/browse/react-dom@0.0.0-experimental-c28f313e6-20220908/cjs/react-dom.development.js)
- [experimental_use(Thenable)](facebook/react#25084)
- [experimental_use(Context)](facebook/react#25202)

types/react/experimental.d.ts

@@ -102,4 +102,31 @@ declare module '.' {
      * @see https://reactjs.org/docs/concurrent-mode-patterns.html#suspenselist
      */
     export const SuspenseList: ExoticComponent<SuspenseListProps>;
+
+    interface ThenableImpl<T> {
+        then(onFulfill: (value: T) => unknown, onReject: (error: unknown) => unknown): void | PromiseLike<unknown>;
+    }
+    interface UntrackedThenable<T> extends ThenableImpl<T> {
+        status?: void;
+    }
+
+    export interface PendingThenable<T> extends ThenableImpl<T> {
+        status: 'pending';
+    }
+
+    export interface FulfilledThenable<T> extends ThenableImpl<T> {
+        status: 'fulfilled';
+        value: T;
+    }
+
+    export interface RejectedThenable<T> extends ThenableImpl<T> {
+        status: 'rejected';
+        reason: unknown;
+    }
+
+    export type Thenable<T> = UntrackedThenable<T> | PendingThenable<T> | FulfilledThenable<T> | RejectedThenable<T>;
+
+    export type Usable<T> = Thenable<T> | Context<T>;
+
+    export function experimental_use<T>(usable: Usable<T>): T;
 }

types/react/test/experimental.tsx

@@ -36,3 +36,19 @@ function suspenseTest() {
     <React.Suspense fallback="Loading">A</React.Suspense>
     <React.Suspense fallback="Loading">B</React.Suspense>
 </React.SuspenseList>;
+
+const contextUsers = React.createContext(['HAL']);
+const promisedUsers = Promise.resolve(['Dave']);
+
+function useUse() {
+    // @ts-expect-error Missing value
+    React.experimental_use();
+
+    // $ExpectType string[]
+    const users = React.experimental_use(promisedUsers);
+    // @ts-expect-error incompatible type. Mainly to potentially inspect TypeScript error message
+    React.experimental_use({});
+
+    // $ExpectType string[]
+    const contextValue = React.experimental_use(contextUsers);
+}