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/language_models/src/provider/copilot_chat.rs

@@ -229,8 +229,8 @@ impl LanguageModel for CopilotChatLanguageModel {
         let is_streaming = copilot_request.stream;
 
         let request_limiter = self.request_limiter.clone();
-        let future = cx.spawn(|cx| async move {
-            let response = CopilotChat::stream_completion(copilot_request, cx);
+        let future = cx.spawn(async move |cx| {
+            let response = CopilotChat::stream_completion(copilot_request, cx.clone());
             request_limiter.stream(async move {
                 let response = response.await?;
                 let stream = response
@@ -264,6 +264,7 @@ impl LanguageModel for CopilotChatLanguageModel {
                         }
                     })
                     .boxed();
+
                 Ok(stream)
             }).await
         });