[Feature Request] Fast HalfToFloat functions for c#

### Describe the feature request

I haven't found any good libraries that do fast HalfToFloat conversions (ie. Float16 to float)

Currently I am just using [the Unity function](https://docs.unity3d.com/ScriptReference/Mathf.HalfToFloat.html):

It would be good to get some fast functions HalfToFloat and FloatToHalf that work on tensors or arrays.

### Describe scenario use case

to convert float16 to float and vice versa.

Start by comparing the requested behavior with Unity's linked Mathf.HalfToFloat reference and locating ONNX Runtime's relevant tensor or array conversion entry points. The issue is complete when fast HalfToFloat and FloatToHalf functions support the requested float16 conversions for tensors or arrays, with performance and correctness checked.

Written by the indexing model from the issue text.