This function is used by coxme. When a random effect is expressed as a sum of variance terms (matrices), it is important that all of them have the same row/column order and the same block structure. This does so, while retaining as much sparsity in the result as possible.
a list, each element of which is a matrix or bdsmatrix object
a vector of dimnames, the target match for matrice's dimnames
a varlist, whose individual elements may have had row/column rearrangment.