agent2: Port edit_file tool (#35844)

TODO:
- [x] Authorization
- [x] Restore tests

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

crates/agent2/src/tools/thinking_tool.rs

@@ -20,6 +20,7 @@ pub struct ThinkingTool;
 
 impl AgentTool for ThinkingTool {
     type Input = ThinkingToolInput;
+    type Output = String;
 
     fn name(&self) -> SharedString {
         "thinking".into()