GitLab

Summary:
* Adds a "max" option for the point_reduction input to the
  chamfer_distance function.
* When combining the x and y directions, maxes the losses instead
  of summing them when point_reduction="max".
* Moves batch reduction to happen after the directions are
  combined.
* Adds test_chamfer_point_reduction_max and
  test_single_directional_chamfer_point_reduction_max tests.

Fixes  https://github.com/facebookresearch/pytorch3d/issues/1838

Reviewed By: bottler

Differential Revision: D60614661

fbshipit-source-id: 7879816acfda03e945bada951b931d2c522756eb