CDK NestedStack: Accessing a nested stack resource in a stack resolves to Amazon.JSII.Runtime.Deputy.AnonymousObject and cannot be casted to CfnStack

### Describe the bug

I have use case that I need to add parameters being provided to a nested stack that is created by an AWS provided EKS construct (in this case the nested stacks containing the Kubectl and resource provider lambda functions). I can find the resources in the node tree, but they cannot be casted to a `CfnStack`, they are of type `Amazon.JSII.Runtime.Deputy.AnonymousObject` and I cannot access the `parameters` property of the stack. This results in having to manipulate the rendered CloudFormation template to achieve the desired outcome.

### Expected Behavior

Be able to access a nested stack resource and cast it to a `CfnStack`.

### Current Behavior

The only available type is `Amazon.JSII.Runtime.Deputy.AnonymousObject`.

### Reproduction Steps

```csharp
FixUpResourceProvider("@aws-cdk--aws-eks.ClusterResourceProvider");
FixUpResourceProvider("@aws-cdk--aws-eks.KubectlProvider");

private void FixUpResourceProvider(string name)
{
IConstruct resourceProviderNestedStack = this.Node.TryFindChild(name);

// Add the parameters to the actual nested stack so it can receive them
if (resourceProviderNestedStack != null)
{
NestedStack nestedStack = resourceProviderNestedStack as NestedStack;

var nestedStackResource = nestedStack.NestedStackResource as CfnStack;

nestedStackResource.Parameters.GetType() == typeof(Amazon.JSII.Runtime.Deputy.AnonymousObject)
}
}
```

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

2.138.0

### Framework Version

_No response_

### Node.js Version

v20.9.0

### OS

darwin

### Language

.NET

### Language Version

_No response_

### Other information

_No response_

Reproduce the issue with the C# snippet against AWS CDK 2.138.0, focusing on NestedStack.NestedStackResource, CfnStack, and the JSII AnonymousObject value. Trace how the nested stack resource is exposed to .NET and determine what is needed for it to be castable and for Parameters to be accessible. Done means the reproduction can access the nested stack as a CfnStack without manipulating the rendered template.

Written by the indexing model from the issue text.