Refactor bvals code

[lroberts36]

The old bvals code relies on a somewhat complex inheritance structure and much of it is unused after changes to the boundary communication routines. We should go through the old code, remove what is unnecessary, and clean things up/shorten code where possible.

[lroberts36]

Some aspirational code for replacing BoundaryBase::SearchAndSetNeighbors (I mostly created this issue so I would have somewhere to stash this):

std::unordered_map<LogicalLocation, NeighborBlock> 
GetNeighborLocationMap(MeshBlockTree &tree, LogicalLocation center_loc) {
  std::unordered_map<LogicalLocation, NeighborBlock> neighbor_map;
  const ind ndim = 3;
  for (int i = -(ndim > 0); i <= (ndim > 0); ++i) {
    for (int j = -(ndim > 1); j <= (ndim > 1); ++j) {
      for (int k = -(ndim > 2); k <= (ndim > 2); ++k) {
        if (i==0 && j==0 && k==0) continue;
        NeighborConnect nc;
        int connect_indicator = std::abs(i) + std::abs(j) + std::abs(k);
        if (connect_indicator == 1) {
          nc = NeighborConnect::face;
        } else if (connect_indicator == 2) {
          nc = NeighborConnect::edge;
        } else if (connect_indicator == 3) {
          nc = NeighborConnect::corner;
        }
        const int bufid = -1; // I am not sure how these need to be set 
        const int tbid = -1; // I am not sure how these need to be set 

        auto pneighbor_tree = tree.FindNeighbor(center_loc, i, j, k);
        if (pneighbor_tree == nullptr) {
          // There is no neighbor in this direction
        } else if (!pneighbor_tree->IsLeaf()) {
          auto xidxs = (i == 0 ? std::vector<int>{0, 1} : std::vector<int>{i < 0});
          auto yidxs = (j == 0 ? std::vector<int>{0, 1} : std::vector<int>{j < 0});
          auto zidxs = (k == 0 ? std::vector<int>{0, 1} : std::vector<int>{k < 0});
          if (ndim < 3) zidxs = {0};
          if (ndim < 2) yidxs = {0};
          if (ndim < 1) xidxs = {0};
          for (auto nox1 : xidxs) {
            for (auto nox2 : yidxs) {
              for (auto nox3 : zidxs) {
                auto pleaf = pneighbor_tree->GetLeaf(nox1, nox2, nox3);
                auto nid = pleaf->GetGid();
                int ifi[2]{0, 0};
                int idx = 0;
                if (xidxs.size() > 1) ifi[idx++] = nox1;
                if (yidxs.size() > 1) ifi[idx++] = nox2;
                if (zidxs.size() > 1) ifi[idx++] = nox3;

                NeighborBlock nb;
                nb.SetNeighbor(pleaf->GetLocation(), ranklist[nid], 
                               pleaf->GetLocation().level, nid, i, j, k,
                               nc, nid - nslist[ranklist[nid]], 
                               bufid, tbid, ifi[0], ifi[1]);
                neighbor_map[pleaf->GetLocation()] = nb;
              }
            }
          }
        } else {
          // Neighbor is at same or coarse level, so we can just grab it
          auto nloc = pneighbor_tree->GetLocation();
          if (neighbor_map.count(nloc) == 0) {
            auto nid = pneighbor_tree->GetLocation();
            NeighborBlock nb;
            nb.SetNeighbor(nloc, ranklist[nid], nloc.level(),
                           nid, i, j, k,
                           nc, nid - nslist[ranklist[nid]], 
                           bufid, tbid, 0, 0);
            neighbor_map[nloc] = nb;
          }
        }
      }
    }
  }
  // Add some code here for determining neighbor ownership
  return neighbor_map;  
}