Show settings file errors on startup (#23817)

Required using a global `LazyLock<Mutex<AppNotifications>>` instead of a
context global because settings errors first occur before initialization
of the notifications global.

Release Notes:

- Errors in settings file are now reported in UI on startup.

crates/workspace/src/workspace.rs

@@ -365,7 +365,6 @@ fn prompt_and_open_paths(app_state: Arc<AppState>, options: PathPromptOptions, c
 
 pub fn init(app_state: Arc<AppState>, cx: &mut App) {
     init_settings(cx);
-    notifications::init(cx);
     theme_preview::init(cx);
 
     cx.on_action(Workspace::close_global);