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/languages/src/rust.rs

@@ -3,7 +3,7 @@ use async_compression::futures::bufread::GzipDecoder;
 use async_trait::async_trait;
 use collections::HashMap;
 use futures::{io::BufReader, StreamExt};
-use gpui::{App, AsyncAppContext, Task};
+use gpui::{App, AsyncApp, Task};
 use http_client::github::AssetKind;
 use http_client::github::{latest_github_release, GitHubLspBinaryVersion};
 pub use language::*;
@@ -78,7 +78,7 @@ impl LspAdapter for RustLspAdapter {
         &self,
         delegate: &dyn LspAdapterDelegate,
         _: Arc<dyn LanguageToolchainStore>,
-        _: &AsyncAppContext,
+        _: &AsyncApp,
     ) -> Option<LanguageServerBinary> {
         let path = delegate.which("rust-analyzer".as_ref()).await?;
         let env = delegate.shell_env().await;