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/assistant_slash_commands/src/auto_command.rs

@@ -5,7 +5,7 @@ use assistant_slash_command::{
 };
 use feature_flags::FeatureFlag;
 use futures::StreamExt;
-use gpui::{App, AsyncAppContext, Task, WeakEntity, Window};
+use gpui::{App, AsyncApp, Task, WeakEntity, Window};
 use language::{CodeLabel, LspAdapterDelegate};
 use language_model::{
     LanguageModelCompletionEvent, LanguageModelRegistry, LanguageModelRequest,
@@ -77,7 +77,7 @@ impl SlashCommand for AutoCommand {
 
         let cx: &mut App = cx;
 
-        cx.spawn(|cx: gpui::AsyncAppContext| async move {
+        cx.spawn(|cx: gpui::AsyncApp| async move {
             let task = project_index.read_with(&cx, |project_index, cx| {
                 project_index.flush_summary_backlogs(cx)
             })?;
@@ -189,7 +189,7 @@ struct CommandToRun {
 async fn commands_for_summaries(
     summaries: &[FileSummary],
     original_prompt: &str,
-    cx: &AsyncAppContext,
+    cx: &AsyncApp,
 ) -> Result<Vec<CommandToRun>> {
     if summaries.is_empty() {
         log::warn!("Inferring no context because there were no summaries available.");

crates/assistant_slash_commands/src/diagnostics_command.rs

@@ -303,7 +303,7 @@ fn collect_diagnostics(
                 .await
                 .log_err()
             {
-                let snapshot = cx.read_model(&buffer, |buffer, _| buffer.snapshot())?;
+                let snapshot = cx.read_entity(&buffer, |buffer, _| buffer.snapshot())?;
                 collect_buffer_diagnostics(&mut output, &snapshot, options.include_warnings);
             }