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/copilot/src/copilot.rs

@@ -11,8 +11,8 @@ use collections::{HashMap, HashSet};
 use command_palette_hooks::CommandPaletteFilter;
 use futures::{channel::oneshot, future::Shared, Future, FutureExt, TryFutureExt};
 use gpui::{
-    actions, App, AppContext as _, AsyncAppContext, Context, Entity, EntityId, EventEmitter,
-    Global, Task, WeakEntity,
+    actions, App, AppContext as _, AsyncApp, Context, Entity, EntityId, EventEmitter, Global, Task,
+    WeakEntity,
 };
 use http_client::github::get_release_by_tag_name;
 use http_client::HttpClient;
@@ -424,7 +424,7 @@ impl Copilot {
         http: Arc<dyn HttpClient>,
         node_runtime: NodeRuntime,
         this: WeakEntity<Self>,
-        mut cx: AsyncAppContext,
+        mut cx: AsyncApp,
     ) {
         let start_language_server = async {
             let server_path = get_copilot_lsp(http).await?;