## Context

This PR builds on https://github.com/zed-industries/zed/pull/52047,
adding support for the new behavior to the keymap editor. The primary
change is replacing usages of `NoAction` with `Unbind` when updating the
users keymap, i.e. deleting/editing default bindings.

This PR does not completely solve the UI challenge of `Unbind`. For now,
we just don't show Unbind entries in the UI, and mark unbound
keybindings as unbound (shown in screenshot).

<img width="3854" height="2230" alt="Screenshot 2026-03-23 at 11 49
42 AM"
src="https://github.com/user-attachments/assets/843856c6-2c94-47c1-be44-21becfdf467e"
/>

## How to Review

- Check behavior changes in keymap updates
- Check UI changes and filters in keymap editor

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## Self-Review Checklist

<!-- Check before requesting review: -->
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A or Added/Fixed/Improved ...