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/project/src/environment.rs

@@ -97,7 +97,7 @@ impl ProjectEnvironment {
 
         if let Some(cli_environment) = self.get_cli_environment() {
             return cx
-                .spawn(|_, _| async move {
+                .spawn(async move |_, _| {
                     let path = cli_environment
                         .get("PATH")
                         .map(|path| path.as_str())
@@ -144,7 +144,7 @@ impl ProjectEnvironment {
     ) -> Task<Option<HashMap<String, String>>> {
         let load_direnv = ProjectSettings::get_global(cx).load_direnv.clone();
 
-        cx.spawn(|this, mut cx| async move {
+        cx.spawn(async move |this, cx| {
             let (mut shell_env, error_message) = cx
                 .background_spawn({
                     let worktree_abs_path = worktree_abs_path.clone();
@@ -169,7 +169,7 @@ impl ProjectEnvironment {
             }
 
             if let Some(error) = error_message {
-                this.update(&mut cx, |this, cx| {
+                this.update(cx, |this, cx| {
                     this.environment_error_messages.insert(worktree_id, error);
                     cx.emit(ProjectEnvironmentEvent::ErrorsUpdated)
                 })