feat(edit): enable predicted outputs for gpt-4o models (#6116)

- Enables [the Predicted Outputs
feature](https://platform.openai.com/docs/guides/predicted-outputs) for
gpt-4o models used with Edit commands.

lib/shared/src/sourcegraph-api/completions/types.ts

@@ -37,6 +37,14 @@ export interface CompletionParameters {
     topP?: number
     model?: string
     stream?: boolean
+    // Configuration for a Predicted Output, which can greatly improve response
+    // times when large parts of the model response are known ahead of time.
+    // https://platform.openai.com/docs/guides/latency-optimization#use-predicted-outputs
+    // https://platform.openai.com/docs/api-reference/chat/create#chat-create-prediction
+    prediction?: {
+        type: 'content'
+        content: string
+    }
 }
 
 export interface SerializedCompletionParameters extends Omit<CompletionParameters, 'messages'> {

vscode/src/edit/provider.ts

@@ -134,6 +134,16 @@ export class EditProvider {
                 stopSequences,
                 maxTokensToSample: contextWindow.output,
             } as CompletionParameters
+
+            if (model.includes('gpt-4o')) {
+                // Use Predicted Output for gpt-4o models.
+                // https://platform.openai.com/docs/guides/predicted-outputs
+                params.prediction = {
+                    type: 'content',
+                    content: this.config.task.original,
+                }
+            }
+
             // Set stream param only when the model is disabled for streaming.
             if (modelsService.isStreamDisabled(model)) {
                 params.stream = false