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/assistant_tools/src/regex_search_tool.rs

@@ -73,7 +73,7 @@ impl Tool for RegexSearchTool {
 
         let results = project.update(cx, |project, cx| project.search(query, cx));
 
-        cx.spawn(|cx| async move {
+        cx.spawn(async move|cx|  {
             futures::pin_mut!(results);
 
             let mut output = String::new();
@@ -86,7 +86,7 @@ impl Tool for RegexSearchTool {
                     continue;
                 }
 
-                buffer.read_with(&cx, |buffer, cx| -> Result<(), anyhow::Error> {
+                buffer.read_with(cx, |buffer, cx| -> Result<(), anyhow::Error> {
                     if let Some(path) = buffer.file().map(|file| file.full_path(cx)) {
                         let mut file_header_written = false;
                         let mut ranges = ranges