Logit-normal or probit-normal as sampling distribution for `stat = "acc"`

[fweber144]

For stat = "acc", it would probably make sense to assume a normal distribution as the sampling distribution for a transformed estimator (transformed from the interval $(0, 1)$ to $(-\infty, \infty)$, similarly to stat = "mse" and stat = "rmse" where the estimators are transformed from $(0, \infty)$ to $(-\infty, \infty)$ in #496), see the discussion at #496 (comment).

Note that stat = "R2" is not concerned by this as it may get negative, see #496 (comment).