Update objc2 crates (#3634)

Changes relevant to Winit:
- `icrate` has been deprecated in favour of separate crates per
  framework, in our case `objc2-foundation` and `objc2-app-kit` (and in
  the future `objc2-ui-kit` on iOS).
- Moved `MainThreadMarker::run_on_main` to free-standing function
  `run_on_main`.
- Changed how features work, this should result in less code that we
  need to compile.
- Enums are now real structs instead of type-aliases and free constants.

src/platform_impl/ios/uikit/gesture_recognizer.rs

@@ -1,8 +1,8 @@
-use icrate::Foundation::{CGFloat, NSInteger, NSObject, NSUInteger};
 use objc2::{
     encode::{Encode, Encoding},
     extern_class, extern_methods, mutability, ClassType,
 };
+use objc2_foundation::{CGFloat, NSInteger, NSObject, NSUInteger};
 
 // https://developer.apple.com/documentation/uikit/uigesturerecognizer
 extern_class!(