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/title_bar/src/title_bar.rs

@@ -642,11 +642,11 @@ impl TitleBar {
             .on_click(move |_, window, cx| {
                 let client = client.clone();
                 window
-                    .spawn(cx, move |mut cx| async move {
+                    .spawn(cx, async move |cx| {
                         client
                             .authenticate_and_connect(true, &cx)
                             .await
-                            .notify_async_err(&mut cx);
+                            .notify_async_err(cx);
                     })
                     .detach();
             })