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/debugger_ui/src/tests.rs

@@ -40,13 +40,21 @@ pub async fn init_test_workspace(
         cx.add_window(|window, cx| Workspace::test_new(project.clone(), window, cx));
 
     let debugger_panel = workspace_handle
-        .update(cx, |_, window, cx| cx.spawn_in(window, DebugPanel::load))
+        .update(cx, |_, window, cx| {
+            cx.spawn_in(window, async move |this, cx| {
+                DebugPanel::load(this, cx.clone()).await
+            })
+        })
         .unwrap()
         .await
         .expect("Failed to load debug panel");
 
     let terminal_panel = workspace_handle
-        .update(cx, |_, window, cx| cx.spawn_in(window, TerminalPanel::load))
+        .update(cx, |_, window, cx| {
+            cx.spawn_in(window, async |this, cx| {
+                TerminalPanel::load(this, cx.clone()).await
+            })
+        })
         .unwrap()
         .await
         .expect("Failed to load terminal panel");