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/scroll/actions.rs

@@ -77,12 +77,12 @@ impl Editor {
         );
 
         self.next_scroll_position = self.next_scroll_position.next();
-        self._scroll_cursor_center_top_bottom_task = cx.spawn(|editor, mut cx| async move {
+        self._scroll_cursor_center_top_bottom_task = cx.spawn(async move |editor, cx| {
             cx.background_executor()
                 .timer(SCROLL_CENTER_TOP_BOTTOM_DEBOUNCE_TIMEOUT)
                 .await;
             editor
-                .update(&mut cx, |editor, _| {
+                .update(cx, |editor, _| {
                     editor.next_scroll_position = NextScrollCursorCenterTopBottom::default();
                 })
                 .ok();