Add automatic type promotion to element-wise ops

Adds automatic type promotion to match the default torch-script behavior for element-wise ops. Debug messages added for the type mismatch and cast.

Messages written to log.
```
DEBUG: [Torch-TensorRT] - Type mismatch for inputs in element-wise operation %3 : Tensor = aten::add(%0, %1, %2): Int32, Float32
DEBUG: [Torch-TensorRT] - Element-wise op type promotion adding cast from Int32 to Float32 for layer %3 : Tensor = aten::add(%0, %1, %2)
```
Fixes # (issue)

Please delete options that are not relevant and/or add your own.

- Bug fix (non-breaking change which fixes an issue)
- New feature (non-breaking change which adds functionality)
- Breaking change (fix or feature that would cause existing functionality to not work as expected)
- This change requires a documentation update

- [ ] My code follows the style guidelines of this project (You can use the linters)
- [ ] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas and hacks
- [ ] I have made corresponding changes to the documentation
- [ ] I have added tests to verify my fix or my feature
- [ ] New and existing unit tests pass locally with my changes
- [ ] I have added the relevant labels to my PR in so that relevant reviewers are notified

Signed-off-by: Michael Feliz <[email protected]>

Author: mfeliz-cruise

core/conversion/converters/converter_util.cpp

@@ -59,6 +59,14 @@ nvinfer1::ITensor* addUnpadding(
   }
 }
 
+nvinfer1::DataType promote_types(nvinfer1::DataType type_a, nvinfer1::DataType type_b){
+  auto torch_type_a = util::TRTDataTypeToScalarType(type_a);
+  auto torch_type_b = util::TRTDataTypeToScalarType(type_b);
+  auto promo_type = at::promote_types(torch_type_a, torch_type_b);
+  auto trt_promo_type = util::ScalarTypeToTRTDataType(promo_type);
+  return trt_promo_type;
+}
+
 nvinfer1::ILayer* add_elementwise(
     ConversionCtx* ctx,
     nvinfer1::ElementWiseOperation op,
@@ -78,6 +86,20 @@ nvinfer1::ILayer* add_elementwise(
     std::swap(self, other);
     swapSelfOther = true;
   }
+
+  if(self->getType() != other->getType()){
+    LOG_DEBUG("Type mismatch for inputs in element-wise operation " << name << ": " << self->getType() << ", " << other->getType());
+    auto promo_type = promote_types(self->getType(), other->getType());
+    if(self->getType() != promo_type){
+      LOG_DEBUG("Element-wise op type promotion adding cast from " << self->getType() << " to " << promo_type << " for layer " << name);
+      self = castITensor(ctx, self, promo_type);
+    }
+    if(other->getType() != promo_type){
+      LOG_DEBUG("Element-wise op type promotion adding cast from " << other->getType() << " to " << promo_type << " for layer " << name);
+      other = castITensor(ctx, other, promo_type);
+    }
+  }
+
   auto selfDim = util::toVec(self->getDimensions());
   auto otherDim = util::toVec(other->getDimensions());
   if (selfDim.size() != otherDim.size()) {