add debug logging for graph region expansion (#141382)
Summary:
This PR adds debug logging for the region expansion algorithm.
X-link: https://github.com/pytorch/pytorch/pull/141382
Approved by: https://github.com/williamwen42
ghstack dependencies: #141381
Reviewed By: clee2000
Differential Revision: D67074357
Pulled By: mlazos
fbshipit-source-id: 0567d5a88ec0f941a9adac0943dd5c8a111e02a5
