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/context_server/src/extension_context_server.rs

@@ -41,16 +41,15 @@ impl ExtensionContextServerProxy for ContextServerFactoryRegistryProxy {
 
                             let id = id.clone();
                             let extension = extension.clone();
-                            cx.spawn(|mut cx| async move {
-                                let extension_project =
-                                    project.update(&mut cx, |project, cx| {
-                                        Arc::new(ExtensionProject {
-                                            worktree_ids: project
-                                                .visible_worktrees(cx)
-                                                .map(|worktree| worktree.read(cx).id().to_proto())
-                                                .collect(),
-                                        })
-                                    })?;
+                            cx.spawn(async move |cx| {
+                                let extension_project = project.update(cx, |project, cx| {
+                                    Arc::new(ExtensionProject {
+                                        worktree_ids: project
+                                            .visible_worktrees(cx)
+                                            .map(|worktree| worktree.read(cx).id().to_proto())
+                                            .collect(),
+                                    })
+                                })?;
 
                                 let command = extension
                                     .context_server_command(id.clone(), extension_project)