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/askpass/src/askpass.rs

@@ -34,9 +34,9 @@ impl AskPassDelegate {
         password_prompt: impl Fn(String, oneshot::Sender<String>, &mut AsyncApp) + Send + Sync + 'static,
     ) -> Self {
         let (tx, mut rx) = mpsc::unbounded::<(String, oneshot::Sender<String>)>();
-        let task = cx.spawn(|mut cx| async move {
+        let task = cx.spawn(async move |cx: &mut AsyncApp| {
             while let Some((prompt, channel)) = rx.next().await {
-                password_prompt(prompt, channel, &mut cx);
+                password_prompt(prompt, channel, cx);
             }
         });
         Self { tx, _task: task }