Use ObjectHandle instead of calling ToString in NLogBeginScopeParser

[snakefoot]

Consider adding support for ObjectHandle in NLog (With Unwrap), instead of the ToString-hack used in #232:

https://github.com/dotnet/corefx/blob/master/src/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.Current.net45.cs

If NLog supports ObjectHandle with Unwrap, then this silly code can be removed:

NLog.Extensions.Logging/src/NLog.Extensions.Logging/Logging/NLogBeginScopeParser.cs

Lines 55 to 58 in 197deb1

	if (state?.GetType().IsSerializable ?? true)
	return NestedDiagnosticsLogicalContext.Push(state);
	else
	return NestedDiagnosticsLogicalContext.Push(state.ToString()); // Support HostingLogScope, ActionLogScope, FormattedLogValues and others

Maybe something like this:

            INestedContext CreateNestedContext(INestedContext parent, T value)
            {
#if NET4_6 || NETSTANDARD
                return new NestedContext<T>(parent, value);
#else
                if (value is IConvertible)
                    return new NestedContext<T>(parent, value);
                else
                    return new NestedContext<System.Runtime.Remoting.ObjectHandle>(parent, new System.Runtime.Remoting.ObjectHandle((object)value));
#endif
            }

            object INestedContext.Value
            {
                get
                {
#if NET4_6 || NETSTANDARD
                    return Value;
#else
                    if (Value is System.Runtime.Remoting.IObjectHandle objectHandle)
                        return objectHandle.Unwrap();
                    else
                        return Value;
#endif
                }
            }

This will also make NLog more user-friendly for others using MDLC and NDLC

[304NotModified]

I don't know much of IObjectHandle , but it sounds good.

Do I need to read into this (IObjectHandle )?

[snakefoot]

@304NotModified Do I need to read into this (IObjectHandle )?

No idea. Can just see that it is the official hack for handling object-sharing across AppDomains. Instead of activating the remoting-serialization for accross-process-communication (Not a remoting or callcontext guru).

Created NLog/NLog#2857 and used the medium-trust test to show that it explodes when given complex objects (But ObjectHandle fixes it).