fix: response to experimental rIC support on Safari removed due to Google Login bug?

packages/frontend/src/scripts/idle-render.ts

@@ -1,3 +1,20 @@
+const requestIdleCallback: typeof globalThis.requestIdleCallback = globalThis.requestIdleCallback ?? (callback) => {
+	const start = performance.now();
+	const timeoutId = setTimeout(() => {
+		callback({
+			didTimeout: false, // polyfill でタイムアウト発火することはない
+			timeRemaining() {
+				const diff = performance.now() - start;
+				return Math.max(0, 50 - diff); // <https://www.w3.org/TR/requestidlecallback/#idle-periods>
+			},
+		});
+	});
+	return timeoutId;
+};
+const cancelIdleCallback: typeof globalThis.cancelIdleCallback = globalThis.cancelIdleCallback ?? (timeoutId) => {
+	clearTimeout(timeoutId);
+};
+
 class IdlingRenderScheduler {
 	#renderers: Set<FrameRequestCallback>;
 	#rafId: number;