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/project/src/lsp_store/clangd_ext.rs

@@ -44,9 +44,9 @@ pub fn register_notifications(
             let adapter = adapter.clone();
             let this = lsp_store;
 
-            move |params: InactiveRegionsParams, mut cx| {
+            move |params: InactiveRegionsParams, cx| {
                 let adapter = adapter.clone();
-                this.update(&mut cx, |this, cx| {
+                this.update(cx, |this, cx| {
                     let diagnostics = params
                         .regions
                         .into_iter()

crates/project/src/lsp_store/rust_analyzer_ext.rs

@@ -51,7 +51,7 @@ pub fn register_notifications(lsp_store: WeakEntity<LspStore>, language_server:
     language_server
         .on_notification::<ServerStatus, _>({
             let name = name.to_string();
-            move |params, mut cx| {
+            move |params, cx| {
                 let this = this.clone();
                 let name = name.to_string();
                 if let Some(ref message) = params.message {
@@ -74,7 +74,7 @@ pub fn register_notifications(lsp_store: WeakEntity<LspStore>, language_server:
                                     lsp_name: name.clone(),
                                 };
                                 let _ = this
-                                    .update(&mut cx, |_, cx| {
+                                    .update(cx, |_, cx| {
                                         cx.emit(LspStoreEvent::LanguageServerPrompt(request));
                                     })
                                     .ok();