helix: Add missing code action menus navigation keymaps (#62356)

# Objective

Helix uses tab/shift-tab to navigate code action menus. Currently, this
will indent the code instead of navigating within the menu.

## Solution

Add keymaps.

## Testing

I tested it manually.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

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Release Notes:

- Added support for using `tab` and `shift-tab` to navigate the code
actions menu in Helix mode