Class.PrivateField
type t('M, 'T) = ('T, t'('M, 'T));
and t'('M, 'T) = {
key: PrivateName.t('M),
value: Property.value('M, 'T),
annot: Type.annotation_or_hint('M, 'T),
static: bool,
variance: option(Variance.t('M)),
comments: option(Syntax.t('M, unit)),
};