Microsoft.Bcl.HashCode 6.0.0 doesn't include `HashCode.AddBytes` from .NET 6

Was this intentional? The implementation, at least [the original version](https://github.com/dotnet/runtime/blob/v6.0.0/src/libraries/System.Private.CoreLib/src/System/HashCode.cs#L316-L334), is compatible with .NET Standard 2.0.