As noted at #26775, we currently allow custom lastindex and firstindex implementations to return non-Int values. For example, Date ranges use an Int64 index, and their last index (and length) cannot always be represented using an Int on 32-bit.

In PR #26775, this required defining lastindex and firstindex in terms of eachindex(IndexLinear(), x) rather than of LinearIndices(x). While it's not really an issue in practice, the fact that LinearIndices is not always able to represent the indices of ranges could be considered as a problem.

Is this really the desired behavior, or should we require that indices be Int?