copilot: Track focus of modal + close modal on ESC (#9217)

I've also made Copilot's modal regain focus whenever you click on it, as
otherwise there's nothing inside of it that can gain focus. Clicks do
not fall through a modal, which I think is nice.



Release Notes:

- Fixed the issue where pressing ESC (`menu::Cancel`) did not exit the
Copilot modal. Fixes #8852

Cargo.lock

@@ -2493,6 +2493,7 @@ dependencies = [
  "fs",
  "gpui",
  "language",
+ "menu",
  "settings",
  "ui",
  "util",