Function S2RegionCoverer.canonicalizeCovering

Modify "covering" if necessary so that it conforms to the current covering parameters (max_cells, min_level, max_level, and level_mod). There are no restrictions on the input S2CellIds (they may be unsorted, overlapping, etc).

s2.s2cell_union.S2CellUnion canonicalizeCovering (
  in const(s2.s2cell_union.S2CellUnion) covering
);