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/gpui_macros/src/derive_render.rs

@@ -11,7 +11,7 @@ pub fn derive_render(input: TokenStream) -> TokenStream {
         impl #impl_generics gpui::Render for #type_name #type_generics
         #where_clause
         {
-            fn render(&mut self, _window: &mut Window, _cx: &mut ModelContext<Self>) -> impl gpui::Element {
+            fn render(&mut self, _window: &mut gpui::Window, _cx: &mut gpui::Context<Self>) -> impl gpui::Element {
                 gpui::Empty
             }
         }