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/terminal/src/terminal.rs

@@ -487,9 +487,9 @@ impl TerminalBuilder {
 
     pub fn subscribe(mut self, cx: &Context<Terminal>) -> Terminal {
         //Event loop
-        cx.spawn(|terminal, mut cx| async move {
+        cx.spawn(async move |terminal, cx| {
             while let Some(event) = self.events_rx.next().await {
-                terminal.update(&mut cx, |terminal, cx| {
+                terminal.update(cx, |terminal, cx| {
                     //Process the first event immediately for lowered latency
                     terminal.process_event(&event, cx);
                 })?;
@@ -527,7 +527,7 @@ impl TerminalBuilder {
                         break 'outer;
                     }
 
-                    terminal.update(&mut cx, |this, cx| {
+                    terminal.update(cx, |this, cx| {
                         if wakeup {
                             this.process_event(&AlacTermEvent::Wakeup, cx);
                         }
@@ -1814,7 +1814,7 @@ impl Terminal {
         if let Some(task) = self.task() {
             if task.status == TaskStatus::Running {
                 let completion_receiver = task.completion_rx.clone();
-                return cx.spawn(|_| async move {
+                return cx.spawn(async move |_| {
                     let _ = completion_receiver.recv().await;
                 });
             }