vim2 (#3594)

- First round of vim tests

Add `observe_keystrokes` back to gpui2
Allow multiple actions to match a given key event

[[PR Description]]

Release Notes:

- (Added|Fixed|Improved) ...
([#<public_issue_number_if_exists>](https://github.com/zed-industries/community/issues/<public_issue_number_if_exists>)).

crates/gpui2/src/platform/test/platform.rs

@@ -130,7 +130,7 @@ impl Platform for TestPlatform {
     }
 
     fn active_window(&self) -> Option<crate::AnyWindowHandle> {
-        unimplemented!()
+        self.active_window.lock().clone()
     }
 
     fn open_window(