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/prettier/src/prettier.rs

@@ -248,7 +248,7 @@ impl Prettier {
         server_id: LanguageServerId,
         prettier_dir: PathBuf,
         node: NodeRuntime,
-        cx: AsyncApp,
+        mut cx: AsyncApp,
     ) -> anyhow::Result<Self> {
         use lsp::{LanguageServerBinary, LanguageServerName};
 
@@ -280,7 +280,7 @@ impl Prettier {
             &prettier_dir,
             None,
             Default::default(),
-            cx.clone(),
+            &mut cx,
         )
         .context("prettier server creation")?;