### Description
* Add std::numeric_limits for MLFloat16 and BFloat16.
* Update some comments in csharp ORTFloat16.shared.cs.
* Add unit tests (including Clip)
Note that the canonical NaN is not consistent in C++ and C#. C# uses
negative quiet NaN as canonical NaN, while C++ uses positive quiet NaN.
The choice of CSharp Float16.NaN is to be consistent with
System.Half.NaN.
FP16 data returns from CUDA might have 7FFF as NaN; FP16 data from CPU
provider might have 0x7E00 as NaN. Anyway there is no consistent
canonical NaN in ORT right now. Because all these NaNs are aligned with
IEEE spec, there shall not an issue in downstream.
### Motivation and Context
std::numeric_limits is used in codebase but not defined for MLFloat16
and BFloat16. It causes some bugs like
https://github.com/microsoft/onnxruntime/issues/21957 introduced by
https://github.com/microsoft/onnxruntime/pull/21493.
### Description
<!-- Describe your changes. -->
Update some testing dependencies.
Fix various warnings. Mainly around documentation (existing) and unit
test usage (mainly resulting from xunit update).
Invalid angle brackets for generics in documentation were changed to use
curly braces based on
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/xmldoc/
> To refer to generic identifiers in code reference (cref) elements, you
can use either the escape characters (for example, cref="List<T>")
or braces (cref="List{T}"). As a special case, the compiler parses the
braces as angle brackets to make the documentation comment less
cumbersome to the author when referring to generic identifiers.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
### Description
Introduce `Float16/BFloat16` support for C# and C++ APIs.
User should be able to perform conversions from `float` to/from
`Float16/BFloat16`, compare values and tests for `NaN, Inifnity, and
whether the number is denormalized.`
### Motivation and Context
User filed issues such as:
https://github.com/microsoft/onnxruntime/issues/14303
