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/journal/src/journal.rs

@@ -118,7 +118,7 @@ pub fn new_journal_entry(workspace: &Workspace, window: &mut Window, cx: &mut Ap
     let view_snapshot = workspace.weak_handle().clone();
 
     window
-        .spawn(cx, |mut cx| async move {
+        .spawn(cx, async move |cx| {
             let (journal_dir, entry_path) = create_entry.await?;
             let opened = if open_new_workspace {
                 let (new_workspace, _) = cx
@@ -132,7 +132,7 @@ pub fn new_journal_entry(workspace: &Workspace, window: &mut Window, cx: &mut Ap
                     })?
                     .await?;
                 new_workspace
-                    .update(&mut cx, |workspace, window, cx| {
+                    .update(cx, |workspace, window, cx| {
                         workspace.open_paths(
                             vec![entry_path],
                             workspace::OpenOptions {
@@ -147,7 +147,7 @@ pub fn new_journal_entry(workspace: &Workspace, window: &mut Window, cx: &mut Ap
                     .await
             } else {
                 view_snapshot
-                    .update_in(&mut cx, |workspace, window, cx| {
+                    .update_in(cx, |workspace, window, cx| {
                         workspace.open_paths(
                             vec![entry_path],
                             workspace::OpenOptions {
@@ -164,7 +164,7 @@ pub fn new_journal_entry(workspace: &Workspace, window: &mut Window, cx: &mut Ap
 
             if let Some(Some(Ok(item))) = opened.first() {
                 if let Some(editor) = item.downcast::<Editor>().map(|editor| editor.downgrade()) {
-                    editor.update_in(&mut cx, |editor, window, cx| {
+                    editor.update_in(cx, |editor, window, cx| {
                         let len = editor.buffer().read(cx).len(cx);
                         editor.change_selections(Some(Autoscroll::center()), window, cx, |s| {
                             s.select_ranges([len..len])