Fix Recent Documents List (continues #8952) (#9919)

@SomeoneToIgnore This code should 100% work for future Zed users, but
for current Zed users, Zed's internal list of recents may not be synced
w/ macOS' Recent Documents at first. If needed this can be fixed by
calling `cx.refresh_recent_documents` on startup, but that feels a bit
unnecessary.

Release Notes:

- Fixes behavior of Recent Documents list on macOS

crates/gpui/src/platform.rs

@@ -118,8 +118,7 @@ pub(crate) trait Platform: 'static {
     fn on_event(&self, callback: Box<dyn FnMut(PlatformInput) -> bool>);
 
     fn set_menus(&self, menus: Vec<Menu>, keymap: &Keymap);
-    fn add_recent_documents(&self, _paths: &[PathBuf]) {}
-    fn clear_recent_documents(&self) {}
+    fn add_recent_document(&self, _path: &Path) {}
     fn on_app_menu_action(&self, callback: Box<dyn FnMut(&dyn Action)>);
     fn on_will_open_app_menu(&self, callback: Box<dyn FnMut()>);
     fn on_validate_app_menu_command(&self, callback: Box<dyn FnMut(&dyn Action) -> bool>);