Add `torch.vdot` (#43004)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/42747
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43004
Reviewed By: mruberry
Differential Revision: D23318935
Pulled By: anjali411
fbshipit-source-id: 12d4824b7cb42bb9ca703172c54ec5c663d9e325
