Move iOS and macOS implementations into new apple module (#3756)

Move iOS and macOS implementations to a shared folder called `apple`, to allow
us to reduce the code-duplication between these platforms in the future.

The folder structure is now:
- `src/platform_impl/apple/`
  - `appkit/`
  - `uikit/`
  - `example_shared_file.rs`
  - `mod.rs`

* Add preliminary support for tvOS, watchOS and visionOS
* Reduce duplication in Cargo.toml when specifying dependencies

src/platform_impl/macos/mod.rs

@@ -1,61 +0,0 @@
-#[macro_use]
-mod util;
-
-mod app;
-mod app_state;
-mod cursor;
-mod event;
-mod event_handler;
-mod event_loop;
-mod ffi;
-mod menu;
-mod monitor;
-mod observer;
-mod view;
-mod window;
-mod window_delegate;
-
-use std::fmt;
-
-pub(crate) use self::event::{physicalkey_to_scancode, scancode_to_physicalkey, KeyEventExtra};
-pub(crate) use self::event_loop::{
-    ActiveEventLoop, EventLoop, EventLoopProxy, OwnedDisplayHandle,
-    PlatformSpecificEventLoopAttributes,
-};
-pub(crate) use self::monitor::{MonitorHandle, VideoModeHandle};
-pub(crate) use self::window::WindowId;
-pub(crate) use self::window_delegate::PlatformSpecificWindowAttributes;
-use crate::event::DeviceId as RootDeviceId;
-
-pub(crate) use self::cursor::CustomCursor as PlatformCustomCursor;
-pub(crate) use self::window::Window;
-pub(crate) use crate::cursor::OnlyCursorImageSource as PlatformCustomCursorSource;
-pub(crate) use crate::icon::NoIcon as PlatformIcon;
-pub(crate) use crate::platform_impl::Fullscreen;
-
-#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct DeviceId;
-
-impl DeviceId {
-    pub const unsafe fn dummy() -> Self {
-        DeviceId
-    }
-}
-
-// Constant device ID; to be removed when if backend is updated to report real device IDs.
-pub(crate) const DEVICE_ID: RootDeviceId = RootDeviceId(DeviceId);
-
-#[derive(Debug)]
-pub enum OsError {
-    CGError(core_graphics::base::CGError),
-    CreationError(&'static str),
-}
-
-impl fmt::Display for OsError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            OsError::CGError(e) => f.pad(&format!("CGError {e}")),
-            OsError::CreationError(e) => f.pad(e),
-        }
-    }
-}