* Split backend_test.in.cpp

* style

* Move backend_{graph_comparison,mlir}.in.cpp back

* Move backend_mlir.in.cpp into backend/ dir

* Disable some tests in PlaidML manifest

* Enable Gather and ScatterAdd to use Eigen kernel for int8 type.

* Reduce number of supported ranks.

* Fix a bug.

*  Use Eigen kernel for ScatterAdd.

* Emit ScatterAdd Eigen kernel for CODEGEN.

Add comments.

Address PR feedback.

* Add more unit tests.

Fix style error.

Add ScatterAdd to AssignOpMap.

* Combine non-scalar cases together.

* Address PR feedback.

* Fix a bug.

* Use reshape to make the shapes of two slices match.

* Rename variables.

Fix bugs.

Use helper function.

Add one unit test.

* Add reshape back.

* Temp save.

* Temp save.

* Temp save.

* Temp save.

* Temp save.

* Temp save.

* Temp save.

* Fix compile errors.

* Fix incorrect index.

* Fix UT typo.

* Interpreter passes UT.

* Fix more bugs.

* Apply style.

* Add shape check for updates tensor.

* Merge typo