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/assistant2/src/context_store.rs

@@ -4,7 +4,7 @@ use std::sync::Arc;
 use anyhow::{anyhow, bail, Result};
 use collections::{BTreeMap, HashMap, HashSet};
 use futures::{self, future, Future, FutureExt};
-use gpui::{App, AsyncApp, Context, Entity, SharedString, Task, WeakEntity};
+use gpui::{App, AppContext as _, AsyncApp, Context, Entity, SharedString, Task, WeakEntity};
 use language::Buffer;
 use project::{ProjectPath, Worktree};
 use rope::Rope;
@@ -456,9 +456,7 @@ fn collect_buffer_info_and_text(
     };
     // Important to collect version at the same time as content so that staleness logic is correct.
     let content = buffer.as_rope().clone();
-    let text_task = cx
-        .background_executor()
-        .spawn(async move { to_fenced_codeblock(&path, content) });
+    let text_task = cx.background_spawn(async move { to_fenced_codeblock(&path, content) });
     (buffer_info, text_task)
 }