Relates to #14723

There's another problematic case,

Variant(variantId = V, constructor = C, value = Unit)

This could represent a value of variant type V with constructor C, where C takes no arguments, e.g.

data V = A Int | B Text | C

var : V
var = C

or a value of variant type V a with constructor C a, where a ~ (), e.g.

data V a = A Int | B Text | C a

var : V ()
var = C ()

There is no way to tell these apart without the type information at hand. We could make the value field of Variant optional, leaving value unset for the former case and set as Unit for the latter, but it's currently commented as Required in https://github.com/digital-asset/daml/blob/main/ledger-api/grpc-definitions/com/daml/ledger/api/v1/value.proto#L146-L148