scalar operands type promotion test

[dan-garvey]

Testing needed for Scalar ops where type promotion is required; cases like f32+f64.

[cathyzhyi]

A new torch op aten::add : (Scalar, Scalar) -> (Scalar) need to be added for purpose of fully testing this.
Refer to existing type promotion examples here: https://github.com/llvm/torch-mlir/blob/main/e2e_testing/torchscript/type_promotion.py

[Vatshank]

Hey @cathyzhyi / @dan-garvey, I am new to torch-mlir and if you folks aren't already working on this, I would like to take a stab at this.

Do we first need to register a new scalar add op following this ATen README here?

And then add tests similar to the ones in this type_promotion test file (which are presently testing 1-d tensors)?

Thanks!