Add tool use support for OpenAI models (#28051)

This PR adds support for using tools to the OpenAI models.

Release Notes:

- agent: Added support for tool use with OpenAI models (Preview only).

crates/language_models/src/provider/cloud.rs

@@ -587,7 +587,7 @@ impl LanguageModel for CloudLanguageModel {
         match self.model {
             CloudModel::Anthropic(_) => true,
             CloudModel::Google(_) => true,
-            CloudModel::OpenAi(_) => false,
+            CloudModel::OpenAi(_) => true,
         }
     }
 
@@ -705,15 +705,13 @@ impl LanguageModel for CloudLanguageModel {
                         },
                     )
                     .await?;
-                    Ok(open_ai::extract_text_from_events(response_lines(response)))
+                    Ok(
+                        crate::provider::open_ai::map_to_language_model_completion_events(
+                            Box::pin(response_lines(response)),
+                        ),
+                    )
                 });
-                async move {
-                    Ok(future
-                        .await?
-                        .map(|result| result.map(LanguageModelCompletionEvent::Text))
-                        .boxed())
-                }
-                .boxed()
+                async move { Ok(future.await?.boxed()) }.boxed()
             }
             CloudModel::Google(model) => {
                 let client = self.client.clone();