Given a uuid of an existing variant alongside a direction, shifts the priority of the variant in the direction.
The values to mutate
The uuid of the variant to shift
The direction to shift the variant in
The mutated values
The variant must exist in the values.
The variant's priority will never be less than 1 as this is reserved for the default variant.
the priority of the default variant will never change from 0.
Given a uuid of an existing variant alongside a direction, shifts the priority of the variant in the direction.