[ONNX] Perform implicit casting of constants for the onnx::where operator (#118733) (#120619)
This PR fixes the problem of having the `Where` operator bound to different types in cases where the dtype is not explicitly set. The PR extends the implicit casting to the onnx::Where operator to fix the issue, and includes the corresponding unit test.
Fixes #118733
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120619
Approved by: https://github.com/BowenBao, https://github.com/thiagocrepaldi
