[Feature Request] get cublashandle in custom op

### Describe the feature request

I find that we can get cublashandle in contrib ops, and can we also get that in custom ops like this?
`cublasHandle_t cublas_handle = reinterpret_cast(ort_.KernelContext_GetCublasHandle(context));`

### Describe scenario use case

complicate custom op

Start by comparing how contrib ops obtain cublasHandle_t with the custom-op path, focusing on KernelContext_GetCublasHandle(context). The requested outcome is equivalent cublas handle access for custom ops; determine the relevant custom-op entry points and how the existing contrib-op behavior is exposed before assessing the required tests.

Written by the indexing model from the issue text.