onnxruntime

[java] CUDA & TensorRT options fix (#20549)

### Description
I misunderstood how UpdateCUDAProviderOptions and
UpdateTensorRTProviderOptions work in the C API, I had assumed that they
updated the options struct, however they re-initialize the struct to the
defaults then only apply the values in the update. I've rewritten the
Java bindings for those classes so that they aggregate all the updates
and apply them in one go. I also updated the C API documentation to note
that these classes have this behaviour. I've not checked if any of the
other providers with an options struct have this behaviour, we only
expose CUDA and TensorRT's options in Java.

There's a small unrelated update to add a private constructor to the
Fp16Conversions classes to remove a documentation warning (they
shouldn't be instantiated anyway as they are utility classes containing
static methods).

### Motivation and Context
Fixes #20544.