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/assistant_tools/src/thinking_tool.rs

@@ -3,7 +3,7 @@ use std::sync::Arc;
 use crate::schema::json_schema_for;
 use anyhow::{Result, anyhow};
 use assistant_tool::{ActionLog, Tool, ToolResult};
-use gpui::{App, Entity, Task};
+use gpui::{AnyWindowHandle, App, Entity, Task};
 use language_model::{LanguageModelRequestMessage, LanguageModelToolSchemaFormat};
 use project::Project;
 use schemars::JsonSchema;
@@ -50,6 +50,7 @@ impl Tool for ThinkingTool {
         _messages: &[LanguageModelRequestMessage],
         _project: Entity<Project>,
         _action_log: Entity<ActionLog>,
+        _window: Option<AnyWindowHandle>,
         _cx: &mut App,
     ) -> ToolResult {
         // This tool just "thinks out loud" and doesn't perform any actions.