Introduce recent files ambient context for assistant (#11791)

<img width="1637" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/5aaec657-3499-42c9-9528-c83728f2a7a1">

Release Notes:

- Added a new ambient context feature that allows showing the model up
to three buffers (along with their diagnostics) that the user interacted
with recently.

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>

crates/gpui/src/window.rs

@@ -200,6 +200,18 @@ impl FocusHandle {
     pub fn contains(&self, other: &Self, cx: &WindowContext) -> bool {
         self.id.contains(other.id, cx)
     }
+
+    /// Dispatch an action on the element that rendered this focus handle
+    pub fn dispatch_action(&self, action: &dyn Action, cx: &mut WindowContext) {
+        if let Some(node_id) = cx
+            .window
+            .rendered_frame
+            .dispatch_tree
+            .focusable_node_id(self.id)
+        {
+            cx.dispatch_action_on_node(node_id, action)
+        }
+    }
 }
 
 impl Clone for FocusHandle {