Function combine_ty_args 

pub fn combine_ty_args<Infcx, I, R>(
    infcx: &Infcx,
    relation: &mut R,
    a_ty: <I as Interner>::Ty,
    b_ty: <I as Interner>::Ty,
    variances: <I as Interner>::VariancesOf,
    a_args: <I as Interner>::GenericArgs,
    b_args: <I as Interner>::GenericArgs,
    mk: impl FnOnce(<I as Interner>::GenericArgs) -> <I as Interner>::Ty,
) -> Result<<I as Interner>::Ty, TypeError<I>>
where
    Infcx: InferCtxtLike<Interner = I>,
    I: Interner,
    R: PredicateEmittingRelation<Infcx>,