Fix missed renames in #22632 (#23688)

Fix a bug where a GPUI macro still used `ModelContext`
Rename `AsyncAppContext` -> `AsyncApp`
Rename update_model, read_model, insert_model, and reserve_model to
update_entity, read_entity, insert_entity, and reserve_entity

Release Notes:

- N/A

crates/assistant_context_editor/src/context_editor.rs

@@ -1217,7 +1217,7 @@ impl ContextEditor {
         let project = this.update(&mut cx, |this, _| this.project.clone())?;
         let resolved_patch = patch.resolve(project.clone(), &mut cx).await;
 
-        let editor = cx.new_window_model(|window, cx| {
+        let editor = cx.new_window_entity(|window, cx| {
             let editor = ProposedChangesEditor::new(
                 patch.title.clone(),
                 resolved_patch