gpui: Refactor PlatformKeyboardLayout (#29653)

Release Notes:

- N/A

crates/gpui/src/platform.rs

@@ -1,4 +1,5 @@
 mod app_menu;
+mod keyboard;
 mod keystroke;
 
 #[cfg(any(target_os = "linux", target_os = "freebsd"))]
@@ -63,6 +64,7 @@ use strum::EnumIter;
 use uuid::Uuid;
 
 pub use app_menu::*;
+pub use keyboard::*;
 pub use keystroke::*;
 
 #[cfg(any(target_os = "linux", target_os = "freebsd"))]
@@ -1679,11 +1681,3 @@ impl From<String> for ClipboardString {
         }
     }
 }
-
-/// A trait for platform-specific keyboard layouts
-pub trait PlatformKeyboardLayout {
-    /// Get the keyboard layout ID, which should be unique to the layout
-    fn id(&self) -> &str;
-    /// Get the keyboard layout display name
-    fn name(&self) -> &str;
-}