Add hashing to bucket-weighted pooling (#20673)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20673
Add option to bucket-weighted pooling to hash the bucket so that any cardinality score can be used.
Reviewed By: huginhuangfb
Differential Revision: D15003509
fbshipit-source-id: 575a149de395f18fd7759f3edb485619f8aa5363
