[dper][pruning] add histogram op (#38514)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38514
this diff introduces the `Histogram` caffe2 op, which computes a histogram tensor for a list of input tensors. the bin edges of the histogram are defined by arg `bin_edges`.
Test Plan: tests
Reviewed By: chocjy
Differential Revision: D21553956
fbshipit-source-id: fc98c8db691d66d2dad57b6ad14867109913cb6f
