Validate that either nodes or index is supplied (but not both) and that
they are of the correct type (non-NA character vector for nodes, non-NA
numeric vector for index).
.validate_nodes_and_index(nodes = NULL, index = NULL)A list with nodes_supplied and index_supplied logical values.
A character vector of node names. If supplied, must be non-NA character vector.
A numeric vector of node indices. If supplied, must be non-NA numeric vector.