Add ; key binding for Helix mode (#34315)

Closes #34111

In Helix mode, the `;` key should collapse the current selection without
moving the cursor. I've added a new action `vim::HelixCollapseSelection`
to support this behavior.


https://github.com/user-attachments/assets/1a40821a-f56f-456e-9d37-532500bef17b

Release Notes:

- Added `;` key binding to collapse the current text selection in Helix
mode

assets/keymaps/vim.json

@@ -377,6 +377,7 @@
     "context": "vim_mode == helix_normal && !menu",
     "bindings": {
       "ctrl-[": "editor::Cancel",
+      ";": "vim::HelixCollapseSelection",
       ":": "command_palette::Toggle",
       "left": "vim::WrappingLeft",
       "right": "vim::WrappingRight",