Fix InstanceServices is null on FunctionBindingContext

[swoog]

I have used FunctionBindingContext with dependency injection.
But I cannot access to the IServiceProvider scoped to the Function instance. The property InstanceServices is null. I think this is a mistake. I do not see a set of this property.

I have test to use _functionInvocationServices directly in my code and the behavior seems to be good.

[gorillapower]

Will this be merged in the next release? Is there a work around for now? I need to access some injected services from my Durable Entity static Run() method.

[swoog]

Actual workaround I used :

var fieldInfo = context.FunctionContext.GetType().GetField("_functionInvocationServices", BindingFlags.Instance | BindingFlags.NonPublic);

if (fieldInfo == null)
{
    throw new ArgumentException("Not found _functionInvocationServices in the Azure Function SDK on FunctionContext (Hack not working)");
}

var serviceProvider = fieldInfo.GetValue(context.FunctionContext) as IServiceProvider;

[eOkadas]

This was exactly what we needed. Thanks @swoog

[mathewc]

Hmmm, looks like this issue has existed since this property was originally added in f7da27d.

Please add a test to the existing FunctionBindingContext test suite that tests this property and potentially others as well.