Updates floor_divide to perform floor division (#78411)
Fixes https://github.com/pytorch/pytorch/issues/43874
This PR changes floor_divide to perform floor division instead of truncation division.
This is a BC-breaking change, but it's a "bug fix," and we've already warned users for several releases this behavior would change.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78411
Approved by: https://github.com/ngimel
