[Feature Request] [C#] Add support for System.Half for input/output tensors

### Describe the feature request

.NET5+ has built-in type System.Half which is similar or equal to OnnxRuntime Float16 type.

### Describe scenario use case

OnnxRuntime allows to use System.Numerics.Tensors for .NET8+ so I heavily rely on it to manipulate input/output data. It also allows you to convert to/from System.Half type but unfortunately OnnxRuntime doesn't support it.

Start by tracing the C# input and output tensor handling relevant to OnnxRuntime's System.Half and Float16 types. The issue names no repository files or tests, so first locate those entry points and their existing type-coverage tests. Done means System.Half works for both input and output tensors, including the .NET8+ System.Numerics.Tensors scenario described.

Written by the indexing model from the issue text.