Fix typo in AppLifecycleState documentation (#54544)

Fixes small typo in AppLifecycleState enum documentation. Documentation to enum references iOS article about managing app lifecycle in UIKit. So, "IOKit" is a misspelled word "UIKit"

I found out Apple has [IOKit framework](https://developer.apple.com/documentation/iokit) but it is not related to app lifecycle

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

lib/ui/platform_dispatcher.dart

@@ -1883,7 +1883,7 @@ class FrameTiming {
 ///   provides state transition callbacks.
 /// * [WidgetsBindingObserver], for a mechanism to observe the lifecycle state
 ///   from the widgets layer.
-/// * iOS's [IOKit activity
+/// * iOS's [UIKit activity
 ///   lifecycle](https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle?language=objc)
 ///   documentation.
 /// * Android's [activity