agent2: Port Zed AI features (#36172)

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>

crates/agent2/src/tests/test_tools.rs

@@ -7,7 +7,7 @@ use std::future;
 #[derive(JsonSchema, Serialize, Deserialize)]
 pub struct EchoToolInput {
     /// The text to echo.
-    text: String,
+    pub text: String,
 }
 
 pub struct EchoTool;