Make "--cuda_version" build arg optional (#15758)
### Description
This change will allow us building CUDA EP without installing CUDA SDK
on Windows.
### Motivation and Context
Nvidia's CUDA installer comes with a VS extension. In the past, we
require installing the extension. It is a little bit inconvenient since:
1. Visual Studio must be installed before CUDA SDK. CUDA's installer
will not install the extension if your machine doesn't have Visual
Studio.
2. We need to install CUDA SDK on our build machines, instead of just
downloading it and using it.
After this change, we will not need to install CUDA SDK on our build
machines. So it will be easier to add a support for a different CUDA
version.
Also, fix two PreFast warnings.
