agent: Render diffs for the edit file tool (#29234)

This PR implements the `ToolCard` for the edit file tool, which allow us
to display an editor with a diff in the thread view with the changes
performed by the model.

- [x] Fix buffer sometimes displaying empty
- [x] Stop buffer from scrolling together with the thread
- [x] Fix multibuffer header sometimes appearing
- [x] Fix buffer height issue
- [x] Implement "full height" expand button
- [x] Add "Jump To File" functionality
- [x] Polish and refine styles

Release Notes:

- agent: Added diff preview cards in the thread view for edits performed
by the agent.

---------

Co-authored-by: João Marcos <marcospb19@hotmail.com>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>
Co-authored-by: Agus Zubiaga <hi@aguz.me>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/agent/src/message_editor.rs

@@ -195,6 +195,7 @@ impl MessageEditor {
                 editor.set_mode(EditorMode::Full {
                     scale_ui_elements_with_buffer_font_size: false,
                     show_active_line_background: false,
+                    sized_by_content: false,
                 })
             } else {
                 editor.set_mode(EditorMode::AutoHeight {
@@ -277,6 +278,7 @@ impl MessageEditor {
         let context_store = self.context_store.clone();
         let git_store = self.project.read(cx).git_store().clone();
         let checkpoint = git_store.update(cx, |git_store, cx| git_store.checkpoint(cx));
+        let window_handle = window.window_handle();
 
         cx.spawn(async move |this, cx| {
             let checkpoint = checkpoint.await.ok();
@@ -333,7 +335,7 @@ impl MessageEditor {
             thread
                 .update(cx, |thread, cx| {
                     thread.advance_prompt_id();
-                    thread.send_to_model(model, cx);
+                    thread.send_to_model(model, Some(window_handle), cx);
                 })
                 .log_err();
         })
@@ -341,9 +343,9 @@ impl MessageEditor {
     }
 
     fn stop_current_and_send_new_message(&mut self, window: &mut Window, cx: &mut Context<Self>) {
-        let cancelled = self
-            .thread
-            .update(cx, |thread, cx| thread.cancel_last_completion(cx));
+        let cancelled = self.thread.update(cx, |thread, cx| {
+            thread.cancel_last_completion(Some(window.window_handle()), cx)
+        });
 
         if cancelled {
             self.set_editor_is_expanded(false, cx);