Implement LengthsToOffsets operator in Caffe2 (#46590)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46590
This operator is very similar to LengthsToRanges but doesn't pack the offsets next to the original lengths.
Reviewed By: yf225
Differential Revision: D24419746
fbshipit-source-id: aa8b014588bb22eced324853c545f8684086c4e4
