Allow ref struct on Generic ThrowHelper methods

### Overview

This would allow ref structs to be used in pattern matching with a `ThrowHelper` case, using the new [allow ref struct](https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters#allows-ref-struct) "anti-constraint".

### API breakdown

This changes nothing except allowable use cases for existing ThrowHelper APIs.

### Usage example

I encountered a situation in my code where I wanted to pattern match and return a `ref struct`. I found I could not use the `ThrowHelper` because it was a `ref struct`.

Here's an example of another imaginable situation utilizing the `Span`.
```cs
Span span = x switch
{
0 => stackalloc int[size],
1 => new int[size],
2 => something.AsSpan(),
_ => ThrowHelper.ThrowArgumentOutOfRangeException>(),
};
```

### Breaking change?

No

### Alternatives

throw without `ThrowHelper`

### Additional context

This will require .NET 9 and C# version 13

### Help us help you

Yes, I'd like to be assigned to work on this item