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/project/src/image_store.rs

@@ -394,7 +394,7 @@ impl ImageStoreImpl for Entity<LocalImageStore> {
                 reload_task: None,
             })?;
 
-            let image_id = cx.read_model(&model, |model, _| model.id)?;
+            let image_id = cx.read_entity(&model, |model, _| model.id)?;
 
             this.update(&mut cx, |this, cx| {
                 image_store.update(cx, |image_store, cx| {