Returns a view that associates each row key with the corresponding map from
column keys to values. Changes to the returned map will update this table.
The returned map does not support put() or putAll(), or
setValue() on its entries.
In contrast, the maps returned by rowMap().get() have the same
behavior as those returned by Table.row(R). Those maps may support setValue(), put(), and putAll().
This method returns a SortedMap, instead of the Map
specified in the Table interface.