Move "async move" a few characters to the left in cx.spawn() (#26758)

This is the core change:
https://github.com/zed-industries/zed/pull/26758/files#diff-044302c0d57147af17e68a0009fee3e8dcdfb4f32c27a915e70cfa80e987f765R1052

TODO:
- [x] Use AsyncFn instead of Fn() -> Future in GPUI spawn methods
- [x] Implement it in the whole app
- [x] Implement it in the debugger 
- [x] Glance at the RPC crate, and see if those box future methods can
be switched over. Answer: It can't directly, as you can't make an
AsyncFn* into a trait object. There's ways around that, but they're all
more complex than just keeping the code as is.
- [ ] Fix platform specific code

Release Notes:

- N/A

crates/repl/src/kernels/remote_kernels.rs

@@ -148,7 +148,7 @@ impl RemoteRunningKernel {
 
         let http_client = cx.http_client();
 
-        window.spawn(cx, |cx| async move {
+        window.spawn(cx, async move |cx| {
             let kernel_id = launch_remote_kernel(
                 &remote_server,
                 http_client.clone(),
@@ -201,12 +201,12 @@ impl RemoteRunningKernel {
             let receiving_task = cx.spawn({
                 let session = session.clone();
 
-                |mut cx| async move {
+                async move |cx| {
                     while let Some(message) = r.next().await {
                         match message {
                             Ok(message) => {
                                 session
-                                    .update_in(&mut cx, |session, window, cx| {
+                                    .update_in(cx, |session, window, cx| {
                                         session.route(&message, window, cx);
                                     })
                                     .ok();
@@ -281,7 +281,7 @@ impl RunningKernel for RemoteRunningKernel {
         let token = self.remote_server.token.clone();
         let http_client = self.http_client.clone();
 
-        window.spawn(cx, |_| async move {
+        window.spawn(cx, async move |_| {
             let request = Request::builder()
                 .method("DELETE")
                 .uri(&url)