language_models: Use `POST /completions` endpoint for Zed provider (#29389)

This PR updates the Zed provider to use the `POST /completions`
endpoint.

There is no functional difference from `POST /completion`, but the
pluralized version reads better.

Release Notes:

- N/A
6bb6be826dMarshall Bowers committed on 4/25/2025, 2:58:02 AM· committed by GitHubparent7d9a55d
1 file changedLine totals unavailable