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/language/src/buffer.rs

@@ -1304,8 +1304,8 @@ impl Buffer {
     pub fn reload(&mut self, cx: &Context<Self>) -> oneshot::Receiver<Option<Transaction>> {
         let (tx, rx) = futures::channel::oneshot::channel();
         let prev_version = self.text.version();
-        self.reload_task = Some(cx.spawn(|this, mut cx| async move {
-            let Some((new_mtime, new_text)) = this.update(&mut cx, |this, cx| {
+        self.reload_task = Some(cx.spawn(async move |this, cx| {
+            let Some((new_mtime, new_text)) = this.update(cx, |this, cx| {
                 let file = this.file.as_ref()?.as_local()?;
                 Some((file.disk_state().mtime(), file.load(cx)))
             })?
@@ -1315,9 +1315,9 @@ impl Buffer {
 
             let new_text = new_text.await?;
             let diff = this
-                .update(&mut cx, |this, cx| this.diff(new_text.clone(), cx))?
+                .update(cx, |this, cx| this.diff(new_text.clone(), cx))?
                 .await;
-            this.update(&mut cx, |this, cx| {
+            this.update(cx, |this, cx| {
                 if this.version() == diff.base_version {
                     this.finalize_last_transaction();
                     this.apply_diff(diff, cx);
@@ -1499,9 +1499,9 @@ impl Buffer {
                 self.reparse = None;
             }
             Err(parse_task) => {
-                self.reparse = Some(cx.spawn(move |this, mut cx| async move {
+                self.reparse = Some(cx.spawn(async move |this, cx| {
                     let new_syntax_map = parse_task.await;
-                    this.update(&mut cx, move |this, cx| {
+                    this.update(cx, move |this, cx| {
                         let grammar_changed =
                             this.language.as_ref().map_or(true, |current_language| {
                                 !Arc::ptr_eq(&language, current_language)
@@ -1566,9 +1566,9 @@ impl Buffer {
             {
                 Ok(indent_sizes) => self.apply_autoindents(indent_sizes, cx),
                 Err(indent_sizes) => {
-                    self.pending_autoindent = Some(cx.spawn(|this, mut cx| async move {
+                    self.pending_autoindent = Some(cx.spawn(async move |this, cx| {
                         let indent_sizes = indent_sizes.await;
-                        this.update(&mut cx, |this, cx| {
+                        this.update(cx, |this, cx| {
                             this.apply_autoindents(indent_sizes, cx);
                         })
                         .ok();

crates/language/src/language_registry.rs

@@ -940,7 +940,7 @@ impl LanguageRegistry {
         server_id: LanguageServerId,
         name: &LanguageServerName,
         binary: lsp::LanguageServerBinary,
-        cx: gpui::AsyncApp,
+        cx: &mut gpui::AsyncApp,
     ) -> Option<lsp::LanguageServer> {
         use gpui::AppContext as _;
 
@@ -951,7 +951,7 @@ impl LanguageRegistry {
             binary,
             name.0.to_string(),
             fake_entry.capabilities.clone(),
-            cx.clone(),
+            cx,
         );
         fake_entry._server = Some(fake_server.clone());