Cherry-picked edit predictions: Fix manually requesting completions
(#24860)
We were disabling edit predictions altogether when
`show_edit_predictions` was set to `false`. However, even in that case,
`editor::ShowEditPrediction` is supposed to let your request a
prediction manually.
Release Notes:
- Fixed `editor::ShowEditPrediction` when `show_edit_predictions` is set
to `false`.
Co-authored-by: Agus Zubiaga <agus@zed.dev>