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/normal/case.rs

@@ -63,7 +63,7 @@ where
                             cursor_positions.push(selection.start..selection.start);
                         }
                     }
-                    Mode::Insert | Mode::Normal => {
+                    Mode::Insert | Mode::Normal | Mode::Replace => {
                         let start = selection.start;
                         let mut end = start;
                         for _ in 0..count {