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/terminals.rs

@@ -115,17 +115,17 @@ impl Project {
         }
         let settings = TerminalSettings::get(settings_location, cx).clone();
 
-        cx.spawn(move |project, mut cx| async move {
+        cx.spawn(async move |project, cx| {
             let python_venv_directory = if let Some(path) = path.clone() {
                 project
-                    .update(&mut cx, |this, cx| {
+                    .update(cx, |this, cx| {
                         this.python_venv_directory(path, settings.detect_venv.clone(), cx)
                     })?
                     .await
             } else {
                 None
             };
-            project.update(&mut cx, |project, cx| {
+            project.update(cx, |project, cx| {
                 project.create_terminal_with_venv(kind, python_venv_directory, window, cx)
             })?
         })
@@ -406,13 +406,13 @@ impl Project {
         venv_settings: VenvSettings,
         cx: &Context<Project>,
     ) -> Task<Option<PathBuf>> {
-        cx.spawn(move |this, mut cx| async move {
+        cx.spawn(async move |this, cx| {
             if let Some((worktree, _)) = this
-                .update(&mut cx, |this, cx| this.find_worktree(&abs_path, cx))
+                .update(cx, |this, cx| this.find_worktree(&abs_path, cx))
                 .ok()?
             {
                 let toolchain = this
-                    .update(&mut cx, |this, cx| {
+                    .update(cx, |this, cx| {
                         this.active_toolchain(
                             worktree.read(cx).id(),
                             LanguageName::new("Python"),
@@ -428,7 +428,7 @@ impl Project {
                 }
             }
             let venv_settings = venv_settings.as_option()?;
-            this.update(&mut cx, move |this, cx| {
+            this.update(cx, move |this, cx| {
                 if let Some(path) = this.find_venv_in_worktree(&abs_path, &venv_settings, cx) {
                     return Some(path);
                 }