_var_index_maps is a vector of maps whose keys are dof_id_types.
Fix a couple more dof_id_type issues in NodalFloodCount.
The 'data' vector and appendPeriodicNeighborNodes() contain dof_id_types.
partial_packed_data stores dof_id_types.
_nodes_visited is a vector of maps whose keys are dof_id_types.