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/git_ui/src/project_diff.rs

@@ -7,7 +7,7 @@ use editor::{scroll::Autoscroll, Editor, EditorEvent, ToPoint};
 use feature_flags::FeatureFlagViewExt;
 use futures::StreamExt;
 use gpui::{
-    actions, AnyElement, AnyView, App, AppContext, AsyncWindowContext, Entity, EventEmitter,
+    actions, AnyElement, AnyView, App, AppContext as _, AsyncWindowContext, Entity, EventEmitter,
     FocusHandle, Focusable, Render, Subscription, Task, WeakEntity,
 };
 use language::{Anchor, Buffer, Capability, OffsetRangeExt, Point};