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/language_model/src/request.rs

@@ -3,7 +3,9 @@ use std::io::{Cursor, Write};
 use crate::role::Role;
 use crate::LanguageModelToolUse;
 use base64::write::EncoderWriter;
-use gpui::{point, size, App, DevicePixels, Image, ObjectFit, RenderImage, Size, Task};
+use gpui::{
+    point, size, App, AppContext as _, DevicePixels, Image, ObjectFit, RenderImage, Size, Task,
+};
 use image::{codecs::png::PngEncoder, imageops::resize, DynamicImage, ImageDecoder};
 use serde::{Deserialize, Serialize};
 use ui::{px, SharedString};
@@ -30,7 +32,7 @@ const ANTHROPIC_SIZE_LIMT: f32 = 1568.;
 
 impl LanguageModelImage {
     pub fn from_image(data: Image, cx: &mut App) -> Task<Option<Self>> {
-        cx.background_executor().spawn(async move {
+        cx.background_spawn(async move {
             match data.format() {
                 gpui::ImageFormat::Png
                 | gpui::ImageFormat::Jpeg