#[derive(VariantEnum)]Expand description
Derives a _Variant enum for the given enum, and derives the VariantEnum trait.
The VariantEnum trait is used to convert an enum into a variant enum, which is an enum that has a variant for
each variant of the input enum, but without any data. This is used for the
VariantSet<T> type, which is a set of variants of type T.
ยงPanics
Panics if the input is not an enum.