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/editor/src/display_map/wrap_map.rs

@@ -198,9 +198,9 @@ impl WrapMap {
                     self.edits_since_sync = self.edits_since_sync.compose(&edits);
                 }
                 Err(wrap_task) => {
-                    self.background_task = Some(cx.spawn(|this, mut cx| async move {
+                    self.background_task = Some(cx.spawn(async move |this, cx| {
                         let (snapshot, edits) = wrap_task.await;
-                        this.update(&mut cx, |this, cx| {
+                        this.update(cx, |this, cx| {
                             this.snapshot = snapshot;
                             this.edits_since_sync = this
                                 .edits_since_sync
@@ -276,9 +276,9 @@ impl WrapMap {
                         self.edits_since_sync = self.edits_since_sync.compose(&output_edits);
                     }
                     Err(update_task) => {
-                        self.background_task = Some(cx.spawn(|this, mut cx| async move {
+                        self.background_task = Some(cx.spawn(async move |this, cx| {
                             let (snapshot, edits) = update_task.await;
-                            this.update(&mut cx, |this, cx| {
+                            this.update(cx, |this, cx| {
                                 this.snapshot = snapshot;
                                 this.edits_since_sync = this
                                     .edits_since_sync