onnxruntime

[js/web] fix test runner with optional input/output (#20399)

### Description
fix test runner with optional input/output.

This change fixes the OP test runner (.jsonc format test) with optional
input(s) and/or output(s).

this fix reveals a problem of dealing with optional outputs:

> Take SkipSimplifiedLayerNorm as example: 
>
> if in the ONNX model, the node's outputs are: [ 'output_0', '' ]
instead of [ 'output_0' ], the current implementation will fail. The
difference is, in the first case, context.outputCount == 2, and then the
typescript implementation will try to create a tensor for output[1]. It
will eventually call to C++ function (OpKernelContext::Output), and the
output.DataRaw() will be nullptr. WebGPU backend will fail because it
cannot deal with a TensorView with data == 0.
>

This problem may need to be fixed or workaround in separated PR. This PR
does not fix this problem. Failed test cases are modified to work -
please note this PR does not break those test cases as they never work.