iOS: Split classes in view.rs into separate files (#3511)

* Move application delegate to its own file
* Move window subclass to window.rs
* Split view controller to separate file

src/platform_impl/ios/app_state.rs

@@ -25,7 +25,7 @@ use objc2::{msg_send, sel};
 use once_cell::sync::Lazy;
 
 use super::uikit::UIView;
-use super::view::WinitUIWindow;
+use super::window::WinitUIWindow;
 use crate::{
     dpi::PhysicalSize,
     event::{Event, InnerSizeWriter, StartCause, WindowEvent},