Identity elimination with graph output (#7312)
* Identity removal
* fix build
* fix build
* fix build
* fix builld
* UTs
* fix UT
* fix UTs
* per comments
* fix UTs
* fix UTs
* per comments
Co-authored-by: Ethan Tao <ettao@OrtTrainingDev4.af05slrtruoetgaxwwjv5nsq5e.px.internal.cloudapp.net>
