gpui: Introduce PlatformKeyboardLayout trait for human-friendly keyboard layout names (#29049)

This PR adds a new `PlatformKeyboardLayout` trait with two methods:
`id(&self) -> &str` and `name(&self) -> &str`. The `id()` method returns
a unique identifier for the keyboard layout, while `name()` provides a
human-readable name. This distinction is especially important on
Windows, where the `id` and `name` can be quite different. For example,
the French layout has an `id` of `0000040C`, which is not
human-readable, whereas the `name` would simply be `French`. Currently,
the existing `keyboard_layout()` method returns what's essentially the
same as `id()` in this new design.

This PR implements the `name()` method for both Windows and macOS. On
Linux, for now, `name()` still returns the same value as `id()`.

Release Notes:

- N/A

crates/gpui/src/platform/linux/x11/client.rs

@@ -59,9 +59,10 @@ use crate::platform::{
 };
 use crate::{
     AnyWindowHandle, Bounds, ClipboardItem, CursorStyle, DisplayId, FileDropEvent, Keystroke,
-    Modifiers, ModifiersChangedEvent, MouseButton, Pixels, Platform, PlatformDisplay,
-    PlatformInput, Point, RequestFrameOptions, ScaledPixels, ScreenCaptureSource, ScrollDelta,
-    Size, TouchPhase, WindowParams, X11Window, modifiers_from_xinput_info, point, px,
+    LinuxKeyboardLayout, Modifiers, ModifiersChangedEvent, MouseButton, Pixels, Platform,
+    PlatformDisplay, PlatformInput, PlatformKeyboardLayout, Point, RequestFrameOptions,
+    ScaledPixels, ScreenCaptureSource, ScrollDelta, Size, TouchPhase, WindowParams, X11Window,
+    modifiers_from_xinput_info, point, px,
 };
 
 /// Value for DeviceId parameters which selects all devices.
@@ -1282,14 +1283,16 @@ impl LinuxClient for X11Client {
         f(&mut self.0.borrow_mut().common)
     }
 
-    fn keyboard_layout(&self) -> String {
+    fn keyboard_layout(&self) -> Box<dyn PlatformKeyboardLayout> {
         let state = self.0.borrow();
         let layout_idx = state.xkb.serialize_layout(STATE_LAYOUT_EFFECTIVE);
-        state
-            .xkb
-            .get_keymap()
-            .layout_get_name(layout_idx)
-            .to_string()
+        Box::new(LinuxKeyboardLayout::new(
+            state
+                .xkb
+                .get_keymap()
+                .layout_get_name(layout_idx)
+                .to_string(),
+        ))
     }
 
     fn displays(&self) -> Vec<Rc<dyn PlatformDisplay>> {