fix(dotnet): Fix property set for nested Dictionaries

[assyadh]

The runtime fails to cast properties when a Dictionary<string, object> is actually a Dictionary<string, Dictionary<string, object>>

Example:

            var launchTemplateData = new CfnLaunchTemplate.LaunchTemplateDataProperty
            {
                InstanceType = "t3.medium",
                Monitoring = new CfnLaunchTemplate.MonitoringProperty { Enabled = true }
            };

            var cfnLaunchTemplate = new CfnLaunchTemplate(stack, "template", new CfnLaunchTemplateProps
            {
                LaunchTemplateData = launchTemplateData,
                LaunchTemplateName = "template"
            });

In this example, the LaunchTemplateData property is a Dictionary<string, object>. However, the 'Monitoring' key is also a Dictionary<string, object>. This was not supported by the runtime and would fail.

Fixes aws/aws-cdk#2496

Cdk synth output after the fix:

Resources:
  template:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateData:
        InstanceType: t3.medium
        Monitoring:
          Enabled: true
      LaunchTemplateName: template
    Metadata:
      aws:cdk:path: HamzaStack/template

Also added a unit test to cover complex properties.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mergify]

The title of this Pull Request does not conform with [Conventional Commits] guidelines. It will need to be adjusted before the PR can be merged.
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[mergify]

Thank you for contributing! ❤️ I will now look into making sure the PR is up-to-date, then proceed to try and merge it!