Harmonize names of `predict_*()` functions and `object$spec$method$*`

[DavisVaughan]

Because having predict_num() go with method$pred is kind of confusing.

Also predict_classprob() goes with method$prob.

[topepo]

The only disconnect now is type = "prob" points to classprob and we'll have to live with that.

[github-actions]

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