Add GivenTensorInt16Fill (#20515)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20515
Needed by the upcoming quantized version of GenerateProposals
Reviewed By: dzhulgakov
Differential Revision: D14430952
fbshipit-source-id: ea852f04cc4b070f8fbe7a1e6535bba4d5b230fd
