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/workspace/src/workspace.rs

@@ -5439,7 +5439,7 @@ impl Render for Workspace {
     fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let mut context = KeyContext::new_with_defaults();
         context.add("Workspace");
-        context.set("keyboard_layout", cx.keyboard_layout().clone());
+        context.set("keyboard_layout", cx.keyboard_layout().name().to_string());
         let centered_layout = self.centered_layout
             && self.center.panes().len() == 1
             && self.active_item(cx).is_some();