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/search/src/project_search.rs

@@ -3795,7 +3795,7 @@ pub mod tests {
         // Wait for the unstaged changes to be loaded
         cx.run_until_parked();
 
-        let buffer_search_bar = cx.new_window_model(|window, cx| {
+        let buffer_search_bar = cx.new_window_entity(|window, cx| {
             let mut search_bar = BufferSearchBar::new(window, cx);
             search_bar.set_active_pane_item(Some(&editor), window, cx);
             search_bar.show(window, cx);