Sketch in assistant edit button (#19705)

Add an edit button to the assistant. This is totally hacked in for now,
just to see how this would feel rendered simply in the UI.

![CleanShot 2024-10-24 at 16 26
14@2x](https://github.com/user-attachments/assets/e630d078-78b7-42d7-93f1-cf61c00bd20e)

cc @as-cii @danilo-leal 

Release Notes:

- N/A

---------

Co-authored-by: Danilo Leal <67129314+danilo-leal@users.noreply.github.com>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>

crates/ui/src/components/keybinding.rs

@@ -184,7 +184,7 @@ pub struct KeyIcon {
 impl RenderOnce for KeyIcon {
     fn render(self, _cx: &mut WindowContext) -> impl IntoElement {
         Icon::new(self.icon)
-            .size(IconSize::Small)
+            .size(IconSize::XSmall)
             .color(Color::Muted)
     }
 }