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/repl/src/repl_store.rs

@@ -122,12 +122,12 @@ impl ReplStore {
         cx: &mut Context<Self>,
     ) -> Task<Result<()>> {
         let kernel_specifications = python_env_kernel_specifications(project, worktree_id, cx);
-        cx.spawn(move |this, mut cx| async move {
+        cx.spawn(async move |this, cx| {
             let kernel_specifications = kernel_specifications
                 .await
                 .map_err(|e| anyhow::anyhow!("Failed to get python kernelspecs: {:?}", e))?;
 
-            this.update(&mut cx, |this, cx| {
+            this.update(cx, |this, cx| {
                 this.kernel_specifications_for_worktree
                     .insert(worktree_id, kernel_specifications);
                 cx.notify();
@@ -149,7 +149,7 @@ impl ReplStore {
                     token,
                 };
                 let http_client = cx.http_client();
-                Some(cx.spawn(|_, _| async move {
+                Some(cx.spawn(async move |_, _| {
                     list_remote_kernelspecs(remote_server, http_client)
                         .await
                         .map(|specs| specs.into_iter().map(KernelSpecification::Remote).collect())
@@ -180,11 +180,11 @@ impl ReplStore {
             anyhow::Ok(all_specs)
         });
 
-        cx.spawn(|this, mut cx| async move {
+        cx.spawn(async move |this, cx| {
             let all_specs = all_specs.await;
 
             if let Ok(specs) = all_specs {
-                this.update(&mut cx, |this, cx| {
+                this.update(cx, |this, cx| {
                     this.kernel_specifications = specs;
                     cx.notify();
                 })