Add TypeScript declarations for requestIdleCallback and cancelIdleCallback

requestIdleCallback and cancelIdleCallback exist at runtime on both
architectures and are declared in the Flow libdefs, but the public
TypeScript types never included them. React Native projects compile
without lib: ["dom"], so the API was invisible to TypeScript users

- Added the declarations to src/types/globals.d.ts
- Add type tests in __typetests__/globals.tsx

Author: Critteros

packages/react-native/__typetests__/globals.tsx

@@ -137,6 +137,25 @@ function testRequestAnimationFrame(){
     );
 }
 
+function testRequestIdleCallback() {
+    let handle = requestIdleCallback(deadline => {
+        const didTimeout: boolean = deadline.didTimeout;
+        const remaining: number = deadline.timeRemaining();
+        console.log(didTimeout, remaining);
+    });
+    cancelIdleCallback(handle);
+
+    handle = requestIdleCallback(noop, { timeout: 100 });
+    cancelIdleCallback(handle);
+
+    // @ts-expect-error
+    requestIdleCallback(noop, { timeout: 'wrong-type' });
+
+    // handle is opaque: object on New Architecture, number on legacy
+    // @ts-expect-error
+    const handleIsNotNumber: number = requestIdleCallback(noop);
+}
+
 const fetchCopy: WindowOrWorkerGlobalScope['fetch'] = fetch;
 
 const myHeaders = new Headers();

packages/react-native/src/types/globals.d.ts

@@ -125,6 +125,16 @@ declare global {
   function cancelAnimationFrame(handle: number | null | undefined): void;
   function requestAnimationFrame(callback: (time: number) => void): number;
 
+  type IdleCallbackID = unknown;
+  function requestIdleCallback(
+    callback: (deadline: {
+      didTimeout: boolean;
+      timeRemaining: () => number;
+    }) => void,
+    options?: {timeout: number},
+  ): IdleCallbackID;
+  function cancelIdleCallback(handle: IdleCallbackID): void;
+
   function fetchBundle(
     bundleId: number,
     callback: (error?: Error | null) => void,