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/project_tree/server_tree.rs

@@ -15,7 +15,7 @@ use std::{
 };
 
 use collections::{HashMap, IndexMap};
-use gpui::{App, AppContext, Entity, Subscription};
+use gpui::{App, AppContext as _, Entity, Subscription};
 use itertools::Itertools;
 use language::{
     language_settings::AllLanguageSettings, Attach, LanguageName, LanguageRegistry,