Reduce amount of unsafe on iOS (#2579)

* Use objc2::foundation CG types

* Add safe abstraction over UIApplication

* Add safe abstraction over UIDevice

* Add safe abstraction over UIScreen

* Add safe abstraction over UIWindow

* Add safe abstraction over UIViewController

* Add safe abstraction over UIView

* Appease clippy

src/platform_impl/ios/uikit/device.rs

@@ -0,0 +1,25 @@
+use objc2::foundation::{MainThreadMarker, NSObject};
+use objc2::rc::{Id, Shared};
+use objc2::{extern_class, extern_methods, msg_send_id, ClassType};
+
+use super::super::ffi::UIUserInterfaceIdiom;
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct UIDevice;
+
+    unsafe impl ClassType for UIDevice {
+        type Super = NSObject;
+    }
+);
+
+extern_methods!(
+    unsafe impl UIDevice {
+        pub fn current(_mtm: MainThreadMarker) -> Id<Self, Shared> {
+            unsafe { msg_send_id![Self::class(), currentDevice] }
+        }
+
+        #[sel(userInterfaceIdiom)]
+        pub fn userInterfaceIdiom(&self) -> UIUserInterfaceIdiom;
+    }
+);