Basic side-by-side diff implementation (#43586)

Release Notes:

- N/A

---------

Co-authored-by: cameron <cameron.studdstreet@gmail.com>
Co-authored-by: Cameron <cameron@zed.dev>

crates/agent_ui/src/agent_diff.rs

@@ -493,7 +493,7 @@ impl Item for AgentDiffPane {
         Some("Assistant Diff Opened")
     }
 
-    fn as_searchable(&self, _: &Entity<Self>) -> Option<Box<dyn SearchableItemHandle>> {
+    fn as_searchable(&self, _: &Entity<Self>, _: &App) -> Option<Box<dyn SearchableItemHandle>> {
         Some(Box::new(self.editor.clone()))
     }
 

crates/agent_ui/src/text_thread_editor.rs

@@ -2556,7 +2556,11 @@ impl Item for TextThreadEditor {
         Some(self.title(cx).to_string().into())
     }
 
-    fn as_searchable(&self, handle: &Entity<Self>) -> Option<Box<dyn SearchableItemHandle>> {
+    fn as_searchable(
+        &self,
+        handle: &Entity<Self>,
+        _: &App,
+    ) -> Option<Box<dyn SearchableItemHandle>> {
         Some(Box::new(handle.clone()))
     }