Function S2CellId.appendAllNeighbors
Append all neighbors of this cell at the given level to "output". Two cells X and Y are neighbors if their boundaries intersect but their interiors do not. In particular, two cells that intersect at a single point are neighbors. Note that for cells adjacent to a face vertex, the same neighbor may be appended more than once.
void appendAllNeighbors(ORangeT)
(
int nbr_level,
ref ORangeT output
) const
if (range .isOutputRange!(ORangeT, S2CellId));
REQUIRES
nbr_level >= this->level().