vim: Add Multi Replace mode in Vim (#8469)

For #4440, I've only added support for normal, if it's visual mode,
would we like this to delete the current selection row and enter insert
mode?

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/vim/src/test.rs

@@ -270,6 +270,11 @@ async fn test_status_indicator(cx: &mut gpui::TestAppContext) {
         cx.workspace(|_, cx| mode_indicator.read(cx).mode),
         Some(Mode::Insert)
     );
+    cx.simulate_keystrokes(["escape", "shift-r"]);
+    assert_eq!(
+        cx.workspace(|_, cx| mode_indicator.read(cx).mode),
+        Some(Mode::Replace)
+    );
 
     // shows even in search
     cx.simulate_keystrokes(["escape", "v", "/"]);