Clean up iOS class declaration (#2462)

* Begin abstraction over UIKit

* Clean up UIWindow override declaration

* Clean up UIApplication delegate declaration

* Clean up UIViewController override declaration

* Finalize objc -> objc2 rename

src/platform_impl/ios/uikit/mod.rs

@@ -0,0 +1,12 @@
+#![deny(unsafe_op_in_unsafe_fn)]
+
+mod responder;
+mod view;
+mod view_controller;
+mod window;
+
+pub(crate) use self::responder::UIResponder;
+#[allow(unused)]
+pub(crate) use self::view::UIView;
+pub(crate) use self::view_controller::UIViewController;
+pub(crate) use self::window::UIWindow;

src/platform_impl/ios/uikit/responder.rs

@@ -0,0 +1,11 @@
+use objc2::foundation::NSObject;
+use objc2::{extern_class, ClassType};
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct UIResponder;
+
+    unsafe impl ClassType for UIResponder {
+        type Super = NSObject;
+    }
+);

src/platform_impl/ios/uikit/view.rs

@@ -0,0 +1,14 @@
+use objc2::foundation::NSObject;
+use objc2::{extern_class, ClassType};
+
+use super::UIResponder;
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct UIView;
+
+    unsafe impl ClassType for UIView {
+        #[inherits(NSObject)]
+        type Super = UIResponder;
+    }
+);

src/platform_impl/ios/uikit/view_controller.rs

@@ -0,0 +1,14 @@
+use objc2::foundation::NSObject;
+use objc2::{extern_class, ClassType};
+
+use super::UIResponder;
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct UIViewController;
+
+    unsafe impl ClassType for UIViewController {
+        #[inherits(NSObject)]
+        type Super = UIResponder;
+    }
+);

src/platform_impl/ios/uikit/window.rs

@@ -0,0 +1,14 @@
+use objc2::foundation::NSObject;
+use objc2::{extern_class, ClassType};
+
+use super::UIResponder;
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct UIWindow;
+
+    unsafe impl ClassType for UIWindow {
+        #[inherits(NSObject)]
+        type Super = UIResponder;
+    }
+);