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/macos/app.rs

@@ -1,13 +1,8 @@
 #![allow(clippy::unnecessary_cast)]
 
-use icrate::AppKit::{
-    NSApplication, NSEvent, NSEventModifierFlagCommand, NSEventTypeKeyUp, NSEventTypeLeftMouseDown,
-    NSEventTypeLeftMouseDragged, NSEventTypeLeftMouseUp, NSEventTypeMouseMoved,
-    NSEventTypeOtherMouseDown, NSEventTypeOtherMouseDragged, NSEventTypeOtherMouseUp,
-    NSEventTypeRightMouseDown, NSEventTypeRightMouseDragged, NSEventTypeRightMouseUp, NSResponder,
-};
-use icrate::Foundation::{MainThreadMarker, NSObject};
 use objc2::{declare_class, msg_send, mutability, ClassType, DeclaredClass};
+use objc2_app_kit::{NSApplication, NSEvent, NSEventModifierFlags, NSEventType, NSResponder};
+use objc2_foundation::{MainThreadMarker, NSObject};
 
 use super::app_delegate::ApplicationDelegate;
 use super::event::flags_contains;
@@ -36,8 +31,8 @@ declare_class!(
             // but that doesn't really matter here.
             let event_type = unsafe { event.r#type() };
             let modifier_flags = unsafe { event.modifierFlags() };
-            if event_type == NSEventTypeKeyUp
-                && flags_contains(modifier_flags, NSEventModifierFlagCommand)
+            if event_type == NSEventType::KeyUp
+                && flags_contains(modifier_flags, NSEventModifierFlags::NSEventModifierFlagCommand)
             {
                 if let Some(key_window) = self.keyWindow() {
                     key_window.sendEvent(event);
@@ -55,10 +50,10 @@ fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent)
     let event_type = unsafe { event.r#type() };
     #[allow(non_upper_case_globals)]
     match event_type {
-        NSEventTypeMouseMoved
-        | NSEventTypeLeftMouseDragged
-        | NSEventTypeOtherMouseDragged
-        | NSEventTypeRightMouseDragged => {
+        NSEventType::MouseMoved
+        | NSEventType::LeftMouseDragged
+        | NSEventType::OtherMouseDragged
+        | NSEventType::RightMouseDragged => {
             let delta_x = unsafe { event.deltaX() } as f64;
             let delta_y = unsafe { event.deltaY() } as f64;
 
@@ -82,13 +77,13 @@ fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent)
                 });
             }
         }
-        NSEventTypeLeftMouseDown | NSEventTypeRightMouseDown | NSEventTypeOtherMouseDown => {
+        NSEventType::LeftMouseDown | NSEventType::RightMouseDown | NSEventType::OtherMouseDown => {
             delegate.queue_device_event(DeviceEvent::Button {
                 button: unsafe { event.buttonNumber() } as u32,
                 state: ElementState::Pressed,
             });
         }
-        NSEventTypeLeftMouseUp | NSEventTypeRightMouseUp | NSEventTypeOtherMouseUp => {
+        NSEventType::LeftMouseUp | NSEventType::RightMouseUp | NSEventType::OtherMouseUp => {
             delegate.queue_device_event(DeviceEvent::Button {
                 button: unsafe { event.buttonNumber() } as u32,
                 state: ElementState::Released,