## Summary

This PR adds a `spacing` method to the context menu, adding the ability
to use the `ListItemSpacing` enum to customize the size of each
individual menu item.

## Self-review

- [x] I've reviewed my diff for quality, security, reliability, and
performance.
- [x] UI changes follow the
[checklist](https://zed.dev/docs/development/ui-checklist).
- [x] Tests cover the new or changed behavior.

Release Notes:

- N/A