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/semantic_index/src/project_index_debug_view.rs

@@ -51,12 +51,12 @@ impl ProjectIndexDebugView {
 
     fn update_rows(&mut self, window: &mut Window, cx: &mut Context<Self>) {
         let worktree_indices = self.index.read(cx).worktree_indices(cx);
-        cx.spawn_in(window, |this, mut cx| async move {
+        cx.spawn_in(window, async move |this, cx| {
             let mut rows = Vec::new();
 
             for index in worktree_indices {
                 let (root_path, worktree_id, worktree_paths) =
-                    index.read_with(&cx, |index, cx| {
+                    index.read_with(cx, |index, cx| {
                         let worktree = index.worktree().read(cx);
                         (
                             worktree.abs_path(),
@@ -73,7 +73,7 @@ impl ProjectIndexDebugView {
                 );
             }
 
-            this.update(&mut cx, |this, cx| {
+            this.update(cx, |this, cx| {
                 this.rows = rows;
                 cx.notify();
             })
@@ -96,7 +96,7 @@ impl ProjectIndexDebugView {
             .embedding_index()
             .chunks_for_path(file_path.clone(), cx);
 
-        cx.spawn_in(window, |this, mut cx| async move {
+        cx.spawn_in(window, async move |this, cx| {
             let chunks = chunks.await?;
             let content = fs.load(&root_path.join(&file_path)).await?;
             let chunks = chunks
@@ -114,7 +114,7 @@ impl ProjectIndexDebugView {
                 })
                 .collect::<Vec<_>>();
 
-            this.update(&mut cx, |this, cx| {
+            this.update(cx, |this, cx| {
                 let view = cx.entity().downgrade();
                 this.selected_path = Some(PathState {
                     path: file_path,