Resolves https://github.com/zed-industries/zed/issues/56129

The edit prediction status bar menu only showed a checkmark for the
active provider when that provider was Zed AI. Non-Zed providers such as
Mercury could be selected and active, but the Providers section rendered
them as unchecked because the toggle condition required `provider =
EditPredictionProvider::Zed`.

This updates the menu condition to show the checkmark for any active
provider, while preserving the existing exception that hides the Zed AI
checkmark when Zed AI is disabled by organization policy.

<div align="center">
<img width="371" height="187" alt="Screenshot 2026-05-08 at 11 27 49 PM"
src="https://github.com/user-attachments/assets/5278a102-bd7d-44a5-a655-74c6ed90b0f9"
/>
</div>

Release Notes:
- Fixed edit prediction provider menu checkmarks for active non-Zed
providers.