Sub in onnx + lean format

[MirkoCalvi]

Current Problem

The "sub" mathematical operation does not respect the onnx format and it is not present any "lean" version of the function

Standard & lean format

The "standard version" of a method is in the format:

    pub fn methodName (args) !Tensor(T) {
       ...
       outputShape = compute output shape...
       outputTensor = compute output tensor...
       ...
       methodName_lean(input, args..., output)

       return outputTensor;
    }

It is suggested to write a get_methodName_oputput_shape() to compute the shape of the output so that the same method can be called during the generation of the readyGraph.

The "lean version" of a method is in the format:

    pub inline fn methodName_lean (args) void {
       ...
       ... actual computation of the output
    }

"lean" and "standard" are mandatory.
The lean version is called during the codegen and the standard version is used in testings.

[huly-for-github]

Connected to Huly®: X_PI-259