Follow-up to14951a5a31* Unify getVariantKindName and getVariantKindForName * Allow each target to specify the preferred case (albeit ignored in MCParser) Note: targets that use variant kinds should call MCExpr::print with a non-null MAI to print variant kinds. operator<< passes a nullptr to `MCExpr::print`, which should be avoided (e.g. Hexagon; fixed in commitcf00ac81ac).