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/vim/src/normal/mark.rs

@@ -147,9 +147,9 @@ impl Vim {
                 cx,
             )
         });
-        cx.spawn_in(window, |this, mut cx| async move {
+        cx.spawn_in(window, async move |this, cx| {
             let editor = task.await?;
-            this.update_in(&mut cx, |_, window, cx| {
+            this.update_in(cx, |_, window, cx| {
                 if let Some(editor) = editor.act_as::<Editor>(cx) {
                     editor.update(cx, |editor, cx| {
                         let map = editor.snapshot(window, cx);