gpui: Allow selection of "Services" menu independent of menu title (#34115)

Release Notes:

- N/A

---

In the same vein as #29538, the "Services" menu on macOS depended on the
text being exactly "Services", not allowing for i18n of the menu name.

This PR introduces a new menu type called `OsMenu` that defines a
special menu that can be populated by the system. Currently, it takes
one enum value, `ServicesMenu` that tells the system to populate its
contents with the items it would usually populate the "Services" menu
with.

An example of this being used has been implemented in the `set_menus`
example:
`cargo run -p gpui --example set_menus`

---

Point to consider:

In `mac/platform.rs:414` the existing code for setting the "Services"
menu remains for backwards compatibility. Should this remain now that
this new method exists to set the menu, or should it be removed?

---------

Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>

crates/gpui/src/platform/app_menu.rs

@@ -20,6 +20,34 @@ impl Menu {
     }
 }
 
+/// OS menus are menus that are recognized by the operating system
+/// This allows the operating system to provide specialized items for
+/// these menus
+pub struct OsMenu {
+    /// The name of the menu
+    pub name: SharedString,
+
+    /// The type of menu
+    pub menu_type: SystemMenuType,
+}
+
+impl OsMenu {
+    /// Create an OwnedOsMenu from this OsMenu
+    pub fn owned(self) -> OwnedOsMenu {
+        OwnedOsMenu {
+            name: self.name.to_string().into(),
+            menu_type: self.menu_type,
+        }
+    }
+}
+
+/// The type of system menu
+#[derive(Copy, Clone, Eq, PartialEq)]
+pub enum SystemMenuType {
+    /// The 'Services' menu in the Application menu on macOS
+    Services,
+}
+
 /// The different kinds of items that can be in a menu
 pub enum MenuItem {
     /// A separator between items
@@ -28,6 +56,9 @@ pub enum MenuItem {
     /// A submenu
     Submenu(Menu),
 
+    /// A menu, managed by the system (for example, the Services menu on macOS)
+    SystemMenu(OsMenu),
+
     /// An action that can be performed
     Action {
         /// The name of this menu item
@@ -53,6 +84,14 @@ impl MenuItem {
         Self::Submenu(menu)
     }
 
+    /// Creates a new submenu that is populated by the OS
+    pub fn os_submenu(name: impl Into<SharedString>, menu_type: SystemMenuType) -> Self {
+        Self::SystemMenu(OsMenu {
+            name: name.into(),
+            menu_type,
+        })
+    }
+
     /// Creates a new menu item that invokes an action
     pub fn action(name: impl Into<SharedString>, action: impl Action) -> Self {
         Self::Action {
@@ -89,10 +128,23 @@ impl MenuItem {
                 action,
                 os_action,
             },
+            MenuItem::SystemMenu(os_menu) => OwnedMenuItem::SystemMenu(os_menu.owned()),
         }
     }
 }
 
+/// OS menus are menus that are recognized by the operating system
+/// This allows the operating system to provide specialized items for
+/// these menus
+#[derive(Clone)]
+pub struct OwnedOsMenu {
+    /// The name of the menu
+    pub name: SharedString,
+
+    /// The type of menu
+    pub menu_type: SystemMenuType,
+}
+
 /// A menu of the application, either a main menu or a submenu
 #[derive(Clone)]
 pub struct OwnedMenu {
@@ -111,6 +163,9 @@ pub enum OwnedMenuItem {
     /// A submenu
     Submenu(OwnedMenu),
 
+    /// A menu, managed by the system (for example, the Services menu on macOS)
+    SystemMenu(OwnedOsMenu),
+
     /// An action that can be performed
     Action {
         /// The name of this menu item
@@ -139,6 +194,7 @@ impl Clone for OwnedMenuItem {
                 action: action.boxed_clone(),
                 os_action: *os_action,
             },
+            OwnedMenuItem::SystemMenu(os_menu) => OwnedMenuItem::SystemMenu(os_menu.clone()),
         }
     }
 }