Start on adding support for editing via the assistant panel (#14795)

Note that this shouldn't have any visible user-facing behavior yet. The
feature is incomplete but we wanna merge early to avoid a long-running
branch.

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/assistant/src/terminal_inline_assistant.rs

@@ -1026,7 +1026,7 @@ impl Codegen {
 
         let telemetry = self.telemetry.clone();
         let model_telemetry_id = prompt.model.telemetry_id();
-        let response = CompletionProvider::global(cx).complete(prompt, cx);
+        let response = CompletionProvider::global(cx).stream_completion(prompt, cx);
 
         self.generation = cx.spawn(|this, mut cx| async move {
             let response = response.await;
@@ -1037,8 +1037,8 @@ impl Codegen {
                     let mut response_latency = None;
                     let request_start = Instant::now();
                     let task = async {
-                        let mut response = response.inner.await?;
-                        while let Some(chunk) = response.next().await {
+                        let mut chunks = response?;
+                        while let Some(chunk) = chunks.next().await {
                             if response_latency.is_none() {
                                 response_latency = Some(request_start.elapsed());
                             }