The end rows of each stripe. The last stripe end is always open-ended, so it's not stored
here. It is invariant that the start row of the stripe is the end row of the previous one
(and is an open boundary for the first one).
Files by stripe. Each element of the list corresponds to stripeEndRow element with the
same index, except the last one. Inside each list, the files are in reverse order by
seqNum. Note that the length of this is one higher than that of stripeEndKeys.