nn.Graph optimizer part 2: add L2, pass job complete, refactor (#5604)

* add valid optimizer case to pass job complete

* refactor and fix optimizer

* support l2 in variable op

* merge master

* format

* fix merge

* rm useless include

* address review

* auto format by CI

* rm internal tensor check after merge master

* restore add loss after merge master

Co-authored-by: oneflow-ci-bot <ci-bot@oneflow.org>