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/settings/src/settings_file.rs

@@ -3,7 +3,6 @@ use fs::Fs;
 use futures::{channel::mpsc, StreamExt};
 use gpui::{App, BackgroundExecutor, ReadGlobal, UpdateGlobal};
 use std::{path::PathBuf, sync::Arc, time::Duration};
-use util::ResultExt;
 
 pub const EMPTY_THEME_NAME: &str = "empty-theme";
 
@@ -73,9 +72,11 @@ pub fn handle_settings_file_changes(
         .block(user_settings_file_rx.next())
         .unwrap();
     SettingsStore::update_global(cx, |store, cx| {
-        store
-            .set_user_settings(&user_settings_content, cx)
-            .log_err();
+        let result = store.set_user_settings(&user_settings_content, cx);
+        if let Err(err) = &result {
+            log::error!("Failed to load user settings: {err}");
+        }
+        settings_changed(result.err(), cx);
     });
     cx.spawn(move |cx| async move {
         while let Some(user_settings_content) = user_settings_file_rx.next().await {