Function cross_variant_member_id 

pub fn cross_variant_member_id(
    group: &CrossVariantGroupId,
    origin_variant: &str,
    language: Language,
    occurrence_rank: u32,
) -> CrossVariantMemberId

Identify one occurrence inside a cross-build-variant group.

Exact duplicates inside one origin are distinguished by a deterministic occurrence rank, never by their path or line anchor.