[SR] Add EliminateTrivialEquallySplit graph pass (#67166)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67166
This optimization is not really the same thing as `FuseListUnpack`, and mixing the logic in that pass is confusing and error-prone. It should really be its own pass.
It's slower since we have to do another pass over the graph, but this is not perf critical code; readability is more important.
Test Plan: Unit tests: `buck test caffe2/benchmarks/static_runtime/...`
Reviewed By: hlu1
Differential Revision: D31887458
fbshipit-source-id: 289e281d512435861fccfe19f017751ad015688c
