Update winit_runner to use spawn_app for wasm32 target (#16630)

# Objective

- Fixes #12562
- Fixes #12195

## Solution

- Use `spawn_app` instead of `run_app` for web platform in
`winit_runner` as suggested in the
[document](https://docs.rs/winit/latest/winit/platform/web/trait.EventLoopExtWebSys.html#tymethod.spawn_app)

## Testing

- Did you test these changes? If so, how?

Tested on web. Created a react app which renders the bevy WASM app and
returns the disposer to JS. Js will call the disposer on component
unmount to stop the app, the disposer sends a signal to a `signal`
receiver in rust which exits the app like this:

```rust
fn handle_stop_signal(
    signal: NonSendMut<StopSignalReceiver>,
    window_entities: Query<(Entity, &Window)>,
    mut event_writer: EventWriter<WindowCloseRequested>,
) {
    if let Ok(_) = signal.try_recv() {
        for (entity, _window) in window_entities.iter() {
            info!("closing window entity: {:x}", entity.to_bits());
            event_writer.send(WindowCloseRequested { window: entity });
        }
    }
}
```


- Are there any parts that need more testing?

  - No

- How can other people (reviewers) test your changes? Is there anything
specific they need to know?

- Are all resources released after stopping the app like this? The WASM
is still loaded, the LogPlugin complains on the logger
re-initialization, but it's a warning anyway.

- If relevant, what platforms did you test these changes on, and are
there any important ones you can't test?

- Tested the WASM version on web platform and the native version on
MacOS.

---------

Co-authored-by: Martín Maita <47983254+mnmaita@users.noreply.github.com>

crates/bevy_winit/src/state.rs

@@ -24,6 +24,8 @@ use bevy_tasks::tick_global_task_pools_on_main_thread;
 use bevy_utils::HashMap;
 use bevy_utils::Instant;
 use core::marker::PhantomData;
+#[cfg(target_arch = "wasm32")]
+use winit::platform::web::EventLoopExtWebSys;
 use winit::{
     application::ApplicationHandler,
     dpi::PhysicalSize,
@@ -868,19 +870,27 @@ pub fn winit_runner<T: Event>(mut app: App) -> AppExit {
     app.world_mut()
         .insert_resource(EventLoopProxyWrapper(event_loop.create_proxy()));
 
-    let mut runner_state = WinitAppRunnerState::new(app);
+    let runner_state = WinitAppRunnerState::new(app);
 
     trace!("starting winit event loop");
-    // TODO(clean): the winit docs mention using `spawn` instead of `run` on Wasm.
+    // The winit docs mention using `spawn` instead of `run` on Wasm.
-    if let Err(err) = event_loop.run_app(&mut runner_state) {
+    // https://docs.rs/winit/latest/winit/platform/web/trait.EventLoopExtWebSys.html#tymethod.spawn_app
-        error!("winit event loop returned an error: {err}");
+    cfg_if::cfg_if! {
+        if #[cfg(target_arch = "wasm32")] {
+            event_loop.spawn_app(runner_state);
+            AppExit::Success
+        } else {
+            let mut runner_state = runner_state;
+            if let Err(err) = event_loop.run_app(&mut runner_state) {
+                error!("winit event loop returned an error: {err}");
+            }
+            // If everything is working correctly then the event loop only exits after it's sent an exit code.
+            runner_state.app_exit.unwrap_or_else(|| {
+                error!("Failed to receive an app exit code! This is a bug");
+                AppExit::error()
+            })
+        }
     }
-
-    // If everything is working correctly then the event loop only exits after it's sent an exit code.
-    runner_state.app_exit.unwrap_or_else(|| {
-        error!("Failed to receive a app exit code! This is a bug");
-        AppExit::error()
-    })
 }
 
 pub(crate) fn react_to_resize(