enhance contrastive loss (#3873)
enhance contrastive loss (#3873)

Signed-off-by: Yiheng Wang <6c538a3af98d7b097509fe1e551ee7cdc81cd4ac@nvidia.com>
Project-MONAI/MONAI,Project-MONAI/MONAI,Project-MONAI/MONAI,Project-MONAI/MONAI