Display what the tool is doing (#27120)

<img width="639" alt="Screenshot 2025-03-19 at 4 56 47 PM"
src="https://github.com/user-attachments/assets/b997f04d-4aff-4070-87b1-ffdb61019bd1"
/>

Release Notes:

- N/A

---------

Co-authored-by: Agus Zubiaga <hi@aguz.me>

crates/assistant_tool/src/assistant_tool.rs

@@ -5,8 +5,7 @@ use std::sync::Arc;
 
 use anyhow::Result;
 use collections::{HashMap, HashSet};
-use gpui::Context;
-use gpui::{App, Entity, SharedString, Task};
+use gpui::{App, Context, Entity, SharedString, Task};
 use language::Buffer;
 use language_model::LanguageModelRequestMessage;
 use project::Project;
@@ -44,6 +43,9 @@ pub trait Tool: 'static + Send + Sync {
         serde_json::Value::Object(serde_json::Map::default())
     }
 
+    /// Returns markdown to be displayed in the UI for this tool.
+    fn ui_text(&self, input: &serde_json::Value) -> String;
+
     /// Runs the tool with the provided input.
     fn run(
         self: Arc<Self>,