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/indent_guides.rs

@@ -111,16 +111,15 @@ impl Editor {
             {
                 Ok(result) => state.active_indent_range = result,
                 Err(future) => {
-                    state.pending_refresh =
-                        Some(cx.spawn_in(window, |editor, mut cx| async move {
-                            let result = cx.background_spawn(future).await;
-                            editor
-                                .update(&mut cx, |editor, _| {
-                                    editor.active_indent_guides_state.active_indent_range = result;
-                                    editor.active_indent_guides_state.pending_refresh = None;
-                                })
-                                .log_err();
-                        }));
+                    state.pending_refresh = Some(cx.spawn_in(window, async move |editor, cx| {
+                        let result = cx.background_spawn(future).await;
+                        editor
+                            .update(cx, |editor, _| {
+                                editor.active_indent_guides_state.active_indent_range = result;
+                                editor.active_indent_guides_state.pending_refresh = None;
+                            })
+                            .log_err();
+                    }));
                     return None;
                 }
             }