FreeBSD support

# Summary
```
Unhandled exception. System.TypeInitializationException: The type initializer for 'Glib.Window' threw an exception.
---> System.PlatformNotSupportedException: Invalid/unsupported operating system.
at Silk.NET.Core.Loader.SearchPathContainer.ThrowInvalidPlatform()
at Silk.NET.Core.Loader.SearchPathContainer.GetLibraryNames()
at Silk.NET.GLFW.Glfw.GetApi()
```

# Steps to reproduce
- Platform: FreeBSD
- Framework Version: .NET 9.0.107 (from pkg install dotnet)
- API: OpenGL
- API Version: 3.3
1. dotnet build anything that uses Silk.NET
2. dotnet run

# Comments
[this](https://github.com/dotnet/Silk.NET/blob/0dc3175e7b3c037c645022030150af022f8be8d9/src/Core/Silk.NET.Core/Loader/SearchPathContainer.cs#L34) does not account for OSPlatform.FreeBSD

[add this to build/nuke/Silk.NET.NUKE.csproj, the is missing for 9.0](https://learn.microsoft.com/en-us/dotnet/standard/serialization/binaryformatter-migration-guide/compatibility-package)

**__If you know how to fix this issue, please submit a pull request instead!__**