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/notebook/notebook_ui.rs

@@ -92,7 +92,9 @@ impl NotebookEditor {
         let language_name = notebook_item.read(cx).language_name();
 
         let notebook_language = notebook_item.read(cx).notebook_language();
-        let notebook_language = cx.spawn_in(window, |_, _| notebook_language).shared();
+        let notebook_language = cx
+            .spawn_in(window, async move |_, _| notebook_language.await)
+            .shared();
 
         let mut cell_order = vec![]; // Vec<CellId>
         let mut cell_map = HashMap::default(); // HashMap<CellId, Cell>
@@ -570,9 +572,9 @@ impl project::ProjectItem for NotebookItem {
         let languages = project.read(cx).languages().clone();
 
         if path.path.extension().unwrap_or_default() == "ipynb" {
-            Some(cx.spawn(|mut cx| async move {
+            Some(cx.spawn(async move |cx| {
                 let abs_path = project
-                    .read_with(&cx, |project, cx| project.absolute_path(&path, cx))?
+                    .read_with(cx, |project, cx| project.absolute_path(&path, cx))?
                     .ok_or_else(|| anyhow::anyhow!("Failed to find the absolute path"))?;
 
                 // todo: watch for changes to the file
@@ -595,7 +597,7 @@ impl project::ProjectItem for NotebookItem {
                 };
 
                 let id = project
-                    .update(&mut cx, |project, cx| project.entry_for_path(&path, cx))?
+                    .update(cx, |project, cx| project.entry_for_path(&path, cx))?
                     .context("Entry not found")?
                     .id;