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/assistant_panel.rs

@@ -356,14 +356,9 @@ impl AssistantPanel {
         &self.thread_store
     }
 
-    fn cancel(
-        &mut self,
-        _: &editor::actions::Cancel,
-        _window: &mut Window,
-        cx: &mut Context<Self>,
-    ) {
+    fn cancel(&mut self, _: &editor::actions::Cancel, window: &mut Window, cx: &mut Context<Self>) {
         self.thread
-            .update(cx, |thread, cx| thread.cancel_last_completion(cx));
+            .update(cx, |thread, cx| thread.cancel_last_completion(window, cx));
     }
 
     fn new_thread(&mut self, action: &NewThread, window: &mut Window, cx: &mut Context<Self>) {