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/collab_ui/src/chat_panel.rs

@@ -199,7 +199,7 @@ impl ChatPanel {
         workspace: WeakEntity<Workspace>,
         cx: AsyncWindowContext,
     ) -> Task<Result<Entity<Self>>> {
-        cx.spawn(|mut cx| async move {
+        cx.spawn(async move |cx| {
             let serialized_panel = if let Some(panel) = cx
                 .background_spawn(async move { KEY_VALUE_STORE.read_kvp(CHAT_PANEL_KEY) })
                 .await
@@ -211,7 +211,7 @@ impl ChatPanel {
                 None
             };
 
-            workspace.update_in(&mut cx, |workspace, window, cx| {
+            workspace.update_in(cx, |workspace, window, cx| {
                 let panel = Self::new(workspace, window, cx);
                 if let Some(serialized_panel) = serialized_panel {
                     panel.update(cx, |panel, cx| {
@@ -867,10 +867,10 @@ impl ChatPanel {
                 })
             });
 
-        cx.spawn(|this, mut cx| async move {
+        cx.spawn(async move |this, cx| {
             let chat = open_chat.await?;
             let highlight_message_id = scroll_to_message_id;
-            let scroll_to_message_id = this.update(&mut cx, |this, cx| {
+            let scroll_to_message_id = this.update(cx, |this, cx| {
                 this.set_active_chat(chat.clone(), cx);
 
                 scroll_to_message_id.or(this.last_acknowledged_message_id)
@@ -881,11 +881,11 @@ impl ChatPanel {
                     ChannelChat::load_history_since_message(chat.clone(), message_id, cx.clone())
                         .await
                 {
-                    this.update(&mut cx, |this, cx| {
+                    this.update(cx, |this, cx| {
                         if let Some(highlight_message_id) = highlight_message_id {
-                            let task = cx.spawn(|this, mut cx| async move {
+                            let task = cx.spawn(async move |this, cx| {
                                 cx.background_executor().timer(Duration::from_secs(2)).await;
-                                this.update(&mut cx, |this, cx| {
+                                this.update(cx, |this, cx| {
                                     this.highlighted_message.take();
                                     cx.notify();
                                 })