settings: Show error notification when settings are invalid (#15905)

https://github.com/user-attachments/assets/07627142-e730-4446-a50b-7ef46f8e661c

We want to improve the design in the future, but it fixes a long
standing paper cut for now.

Release Notes:

- Added a popup that is displayed when the settings are invalid

---------

Co-authored-by: Thorsten <thorsten@zed.dev>

crates/settings/src/settings_file.rs

@@ -1,4 +1,5 @@
 use crate::{settings_store::SettingsStore, Settings};
+use anyhow::Result;
 use fs::Fs;
 use futures::{channel::mpsc, StreamExt};
 use gpui::{AppContext, BackgroundExecutor, ReadGlobal, UpdateGlobal};
@@ -66,6 +67,7 @@ pub fn watch_config_file(
 pub fn handle_settings_file_changes(
     mut user_settings_file_rx: mpsc::UnboundedReceiver<String>,
     cx: &mut AppContext,
+    settings_changed: impl Fn(Result<()>, &mut AppContext) + 'static,
 ) {
     let user_settings_content = cx
         .background_executor()
@@ -79,9 +81,11 @@ pub fn handle_settings_file_changes(
     cx.spawn(move |mut cx| async move {
         while let Some(user_settings_content) = user_settings_file_rx.next().await {
             let result = cx.update_global(|store: &mut SettingsStore, 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, cx);
                 cx.refresh();
             });
             if result.is_err() {