Fix NodeDefDataTypeAttributeName for Unary and Binary op converters.

[drivanov]

• To check the input data type, we need to know which attribute of the node defines it. The op converter defines NodeDefDataTypeAttributeName() to return the name of the attribute.
• The actual converters can override this. If an empty string is returned by NodeDefDataTypeAttributeName then type checking is skipped.
• Previously the unary and binary op converters returned empty string.
  This bug is corrected in this PR.

[tfeher]

Thanks Andrei for the fix! The PR looks good to me.

Please change the PR Title: Fix NodeDafDataTypeAttributeName for Unary and Binary op converters.

Please change the PR description:

• To check the input data type, we need to know which attribute of the node defines it. The op converter defines NodeDefDataTypeAttributeName() to return the name of the attribute.
• The actual converters can override this. If an empty string is returned by NodeDefDataTypeAttributeName then type checking is skipped.
• Previously the unary and binary op converters returned empty string.
  This bug is corrected in this PR.

We will create a separate PR for improving the unit test to catch such errors.

[bixia1]

Compilation error:
third_party/tensorflow/compiler/tf2tensorrt/convert/ops/einsum.cc:706:40: error: no matching function for call to 'ConvertMatMulImpl'
StatusOr result = ConvertMatMulImpl(
^~~~~~~~~~~~~~~~~
./third_party/tensorflow/compiler/tf2tensorrt/convert/convert_nodes.h:566:27: note: candidate function not viable: 1st argument ('const OpConverterParams const') would lose const qualifier
StatusOr ConvertMatMulImpl(OpConverterParams params,
^

[drivanov]

CORRECTED.

[bixia1]

There are still similar errors:
third_party/tensorflow/compiler/tf2tensorrt/convert/ops/einsum.cc:713:24: error: no matching function for call to 'ShuffleEinsumOutput'
TF_RETURN_IF_ERROR(ShuffleEinsumOutput(
^~~~~~~~~~~~~~~~~~~
./third_party/tensorflow/core/platform/errors.h:125:37: note: expanded from macro 'TF_RETURN_IF_ERROR'
::tensorflow::Status _status = (VA_ARGS);
^~~~~~~~~~~
third_party/tensorflow/compiler/tf2tensorrt/convert/ops/einsum.cc:513:8: note: candidate function not viable: 1st argument ('const OpConverterParams const') would lose const qualifier
Status ShuffleEinsumOutput(OpConverterParams params, EinsumDescriptor desc_a,
^

[drivanov]

FIXED