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/language/src/language_registry.rs

@@ -904,7 +904,7 @@ impl LanguageRegistry {
         server_id: LanguageServerId,
         name: &LanguageServerName,
         binary: lsp::LanguageServerBinary,
-        cx: gpui::AsyncAppContext,
+        cx: gpui::AsyncApp,
     ) -> Option<lsp::LanguageServer> {
         let mut state = self.state.write();
         let fake_entry = state.fake_server_entries.get_mut(&name)?;