apple: Implement wake-ups using system mechanisms (#4146)

Do the wake-up inside the perform callback on `CFRunLoopSource`.

src/platform_impl/apple/mod.rs

@@ -3,6 +3,7 @@
 #[cfg(target_os = "macos")]
 mod appkit;
 mod event_handler;
+mod event_loop_proxy;
 mod notification_center;
 #[cfg(not(target_os = "macos"))]
 mod uikit;