feature request: `_prep_inputs_for_prediction_and_return_scores` to become public interface point

[fkiraly]

The AFT models are neat, though there does not seem to be a public interface point from which the paramters of the predictive (parametric) distributions could be queried.

I request that the current private interface point for this, _prep_inputs_for_prediction_and_return_scores, become public, perhaps with:

• a clearer name, such as predict_proba_params
• a unified return, e.g., returning a dict with {"paramname": paramvalue} format

[fkiraly]

I would be happy to contribute this, if you think this is a good idea, @CamDavidsonPilon