Use proper context to show terminal split menu bindings (#21253)

Follow-up of https://github.com/zed-industries/zed/pull/21251

Show proper keybindings on the terminal split button:

<img width="249" alt="image"
src="https://github.com/user-attachments/assets/b51b183f-788a-4e8f-9fec-3ec07f084bd4">

Release Notes:

- N/A