cx.background_executor().spawn(...) -> cx.background_spawn(...) (#25103)

Done automatically with

> ast-grep -p '$A.background_executor().spawn($B)' -r
'$A.background_spawn($B)' --update-all --globs "\!crates/gpui"

Followed by:

* `cargo fmt`
* Unexpected need to remove some trailing whitespace.
* Manually adding imports of `gpui::{AppContext as _}` which provides
`background_spawn`
* Added `AppContext as _` to existing use of `AppContext`

Release Notes:

- N/A

crates/project/src/toolchain_store.rs

@@ -325,16 +325,15 @@ impl LocalToolchainStore {
                 .ok()?
                 .await;
 
-            cx.background_executor()
-                .spawn(async move {
-                    let language = registry
-                        .language_for_name(language_name.as_ref())
-                        .await
-                        .ok()?;
-                    let toolchains = language.toolchain_lister()?;
-                    Some(toolchains.list(root.to_path_buf(), project_env).await)
-                })
-                .await
+            cx.background_spawn(async move {
+                let language = registry
+                    .language_for_name(language_name.as_ref())
+                    .await
+                    .ok()?;
+                let toolchains = language.toolchain_lister()?;
+                Some(toolchains.list(root.to_path_buf(), project_env).await)
+            })
+            .await
         })
     }
     pub(crate) fn active_toolchain(