assistant2: Add tool selector (#26480)

This PR adds a tool selector to Assistant 2 to facilitate customizing
the tools that the model sees:

<img width="1297" alt="Screenshot 2025-03-11 at 4 25 31 PM"
src="https://github.com/user-attachments/assets/7a656343-83bc-4546-9430-6a5f7ff1fd08"
/>

Release Notes:

- N/A

crates/assistant_tool/src/assistant_tool.rs

@@ -14,7 +14,7 @@ pub fn init(cx: &mut App) {
     ToolRegistry::default_global(cx);
 }
 
-#[derive(Debug, PartialEq, Eq, Clone)]
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone)]
 pub enum ToolSource {
     /// A native tool built-in to Zed.
     Native,