Checks whether the geometries of the shapes specified via tm_shape() are
valid. Invalid geometries can cause errors or maps with artifacts.
Details
This tmap element checks the geometries with sf::st_is_valid() and, if
needed, applies sf::st_make_valid(). If that is unsuccessful, it toggles the
s2 backend of the sf package (on or off, depending on whether it was
already enabled) and tries again. If the geometries are still invalid, the map
is drawn with a warning and the invalid geometries are removed.
