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/menu.rs

@@ -1,107 +0,0 @@
-use objc2::rc::Retained;
-use objc2::runtime::Sel;
-use objc2::sel;
-use objc2_app_kit::{NSApplication, NSEventModifierFlags, NSMenu, NSMenuItem};
-use objc2_foundation::{ns_string, MainThreadMarker, NSProcessInfo, NSString};
-
-struct KeyEquivalent<'a> {
-    key: &'a NSString,
-    masks: Option<NSEventModifierFlags>,
-}
-
-pub fn initialize(app: &NSApplication) {
-    let mtm = MainThreadMarker::from(app);
-    let menubar = NSMenu::new(mtm);
-    let app_menu_item = NSMenuItem::new(mtm);
-    menubar.addItem(&app_menu_item);
-
-    let app_menu = NSMenu::new(mtm);
-    let process_name = NSProcessInfo::processInfo().processName();
-
-    // About menu item
-    let about_item_title = ns_string!("About ").stringByAppendingString(&process_name);
-    let about_item =
-        menu_item(mtm, &about_item_title, Some(sel!(orderFrontStandardAboutPanel:)), None);
-
-    // Services menu item
-    let services_menu = NSMenu::new(mtm);
-    let services_item = menu_item(mtm, ns_string!("Services"), None, None);
-    services_item.setSubmenu(Some(&services_menu));
-
-    // Separator menu item
-    let sep_first = NSMenuItem::separatorItem(mtm);
-
-    // Hide application menu item
-    let hide_item_title = ns_string!("Hide ").stringByAppendingString(&process_name);
-    let hide_item = menu_item(
-        mtm,
-        &hide_item_title,
-        Some(sel!(hide:)),
-        Some(KeyEquivalent { key: ns_string!("h"), masks: None }),
-    );
-
-    // Hide other applications menu item
-    let hide_others_item_title = ns_string!("Hide Others");
-    let hide_others_item = menu_item(
-        mtm,
-        hide_others_item_title,
-        Some(sel!(hideOtherApplications:)),
-        Some(KeyEquivalent {
-            key: ns_string!("h"),
-            masks: Some(
-                NSEventModifierFlags::NSEventModifierFlagOption
-                    | NSEventModifierFlags::NSEventModifierFlagCommand,
-            ),
-        }),
-    );
-
-    // Show applications menu item
-    let show_all_item_title = ns_string!("Show All");
-    let show_all_item =
-        menu_item(mtm, show_all_item_title, Some(sel!(unhideAllApplications:)), None);
-
-    // Separator menu item
-    let sep = NSMenuItem::separatorItem(mtm);
-
-    // Quit application menu item
-    let quit_item_title = ns_string!("Quit ").stringByAppendingString(&process_name);
-    let quit_item = menu_item(
-        mtm,
-        &quit_item_title,
-        Some(sel!(terminate:)),
-        Some(KeyEquivalent { key: ns_string!("q"), masks: None }),
-    );
-
-    app_menu.addItem(&about_item);
-    app_menu.addItem(&sep_first);
-    app_menu.addItem(&services_item);
-    app_menu.addItem(&hide_item);
-    app_menu.addItem(&hide_others_item);
-    app_menu.addItem(&show_all_item);
-    app_menu.addItem(&sep);
-    app_menu.addItem(&quit_item);
-    app_menu_item.setSubmenu(Some(&app_menu));
-
-    unsafe { app.setServicesMenu(Some(&services_menu)) };
-    app.setMainMenu(Some(&menubar));
-}
-
-fn menu_item(
-    mtm: MainThreadMarker,
-    title: &NSString,
-    selector: Option<Sel>,
-    key_equivalent: Option<KeyEquivalent<'_>>,
-) -> Retained<NSMenuItem> {
-    let (key, masks) = match key_equivalent {
-        Some(ke) => (ke.key, ke.masks),
-        None => (ns_string!(""), None),
-    };
-    let item = unsafe {
-        NSMenuItem::initWithTitle_action_keyEquivalent(mtm.alloc(), title, selector, key)
-    };
-    if let Some(masks) = masks {
-        item.setKeyEquivalentModifierMask(masks)
-    }
-
-    item
-}