debugger: Fix deadlock in on_app_quit with debugger running (#29372)

This fixes a deadlock that would occur when `DapStore` had its on quit
handler called. The deadlock was caused by `DapStore` spawning on the
main thread while `App::shutdown` blocks the main thread.

We added a debug_panic in GPUI that panics if a foreground task is
spawned while the App context is shutting down. This will help tests
catch hangs in `cx.on_app_quit` calls.

Release Notes:

- N/A

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/project/src/debugger/session.rs

@@ -700,6 +700,7 @@ impl Session {
                 BreakpointStoreEvent::ActiveDebugLineChanged => {}
             })
             .detach();
+            cx.on_app_quit(Self::on_app_quit).detach();
 
             let this = Self {
                 mode: Mode::Building,
@@ -1510,6 +1511,16 @@ impl Session {
         }
     }
 
+    fn on_app_quit(&mut self, cx: &mut Context<Self>) -> Task<()> {
+        let debug_adapter = self.adapter_client();
+
+        cx.background_spawn(async move {
+            if let Some(client) = debug_adapter {
+                client.shutdown().await.log_err();
+            }
+        })
+    }
+
     pub fn shutdown(&mut self, cx: &mut Context<Self>) -> Task<()> {
         self.is_session_terminated = true;
         self.thread_states.exit_all_threads();