Implement Helix Support (WIP) (#19175)

Closes #4642 

- Added the ability to switch to helix normal mode, with an additional
helix visual mode.
- <kbd>ctrl</kbd><kbd>h</kbd> from Insert mode goes to Helix Normal
mode. <kbd> i </kbd> and <kbd> a </kbd> to go back.
- Need to find a way to perform the helix normal mode selection with
<kbd> w </kbd>, <kbd>e </kbd>, <kbd> b </kbd> as a first step. Need to
figure out how the mode will interoperate with the VIM mode as the new
additions are in the same crate.

crates/vim/src/normal/case.rs

@@ -145,6 +145,8 @@ impl Vim {
                             cursor_positions.push(selection.start..selection.start);
                         }
                     }
+
+                    Mode::HelixNormal => {}
                     Mode::Insert | Mode::Normal | Mode::Replace => {
                         let start = selection.start;
                         let mut end = start;