Add last window closed setting (#25185)

Release Notes:

- Added an `on_last_window_closed` setting, that allows users to quit
the app when the last window is closed

---------

Co-authored-by: Richard <richard@zed.dev>

crates/zed/src/zed.rs

@@ -104,6 +104,19 @@ pub fn init(cx: &mut App) {
     }
 }
 
+fn bind_on_window_closed(cx: &mut App) -> Option<gpui::Subscription> {
+    WorkspaceSettings::get_global(cx)
+        .on_last_window_closed
+        .is_quit_app()
+        .then(|| {
+            cx.on_window_closed(|cx| {
+                if cx.windows().is_empty() {
+                    cx.quit();
+                }
+            })
+        })
+}
+
 pub fn build_window_options(display_uuid: Option<Uuid>, cx: &mut App) -> WindowOptions {
     let display = display_uuid.and_then(|uuid| {
         cx.displays()
@@ -144,6 +157,12 @@ pub fn initialize_workspace(
     prompt_builder: Arc<PromptBuilder>,
     cx: &mut App,
 ) {
+    let mut _on_close_subscription = bind_on_window_closed(cx);
+    cx.observe_global::<SettingsStore>(move |cx| {
+        _on_close_subscription = bind_on_window_closed(cx);
+    })
+    .detach();
+
     cx.observe_new(move |workspace: &mut Workspace, window, cx| {
         let Some(window) = window else {
             return;