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/zed/src/zed.rs

@@ -956,7 +956,7 @@ fn install_cli(
                 Some(LINUX_PROMPT_DETAIL),
                 &["Ok"],
             );
-            cx.background_executor().spawn(prompt).detach();
+            cx.background_spawn(prompt).detach();
             return Ok(());
         }
         let path = install_cli::install_cli(cx.deref())
@@ -1335,7 +1335,7 @@ fn show_markdown_app_notification<F>(
 ) where
     F: 'static + Send + Sync + Fn(&mut Window, &mut Context<MessageNotification>),
 {
-    let parsed_markdown = cx.background_executor().spawn(async move {
+    let parsed_markdown = cx.background_spawn(async move {
         let file_location_directory = None;
         let language_registry = None;
         markdown_preview::markdown_parser::parse_markdown(