Tmr stencil matrices may contain unused rows

[manuelkNVDA]

The Far::PatchBuilder used to generate the subdivision weights will produce patch points for every level of isolation, but there may not be any sub-patch generated in the hierarchy (likely rare). This results in stencil matrices storing rows of weights that are never used.

• quantify the number of unused stencil rows in a sizeable topology map
• if significant enough, implement a post-processing pass in Tmr::SubdivisionPlanBuilder to excise the rows & re-index the patch point indices.