(ec2): import an existing AutoScalingGroup with a Role

I'm trying to referring an existing AutoScalingGroup from my CodeDeploy with AutoScalingGroup.**from_auto_scaling_group_name** static method in order to integrate with CodePipeline for automating EC2/On-premise deployment. However, the Role from AutoScalingGroup is not being imported.

### Reproduction Steps

- Refer existing AutoScaling Group:
`asg_1 = autoscaling.AutoScalingGroup.from_auto_scaling_group_name(self, "AutoScaleGroup", "WSAutoscaleStack-webServerAsgIdASG12345-XXXXXX")`

- EC2 Deployment Groups:
`deployment_group = codedeploy.ServerDeploymentGroup(self, "CodeDeployDeploymentGroup", deployment_group_name="MyDeploymentGroup", install_agent=True, auto_scaling_groups=[asg_1])`

### What did you expect to happen?

Ideally, the referenced resource should be imported as an object, so that I can use it all dependents including iam.role from the resource. (c.f. from CodeDeploy Application Environment configuration, choose the Amazon EC2 Auto Scaling group where the current application revision is deployed)

### What actually happened?

The error that I'm getting is as follows:
`jsii.errors.JSIIError: Cannot get policy fragment of AMIPipelineStack/AutoScaleGroup, resource imported without a role`

### Environment

- **CDK CLI Version :** 1.94.0 (build 2c1c0eb)
- **Framework Version:**
- **Node.js Version:** v15.11.0
- **OS :** macOS Catalina
- **Language (Version):** Python (3.8.7)

### Other

This issue was posted and confirmed. The issue is linked,
https://stackoverflow.com/questions/66748035/refer-import-existing-autoscalinggroup-resource-from-cdk-stack

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This is :bug: Bug Report

Start with AutoScalingGroup.from_auto_scaling_group_name and the CodeDeploy ServerDeploymentGroup integration described in the reproduction. Trace how the imported AutoScalingGroup handles its role and compare that with the policy-fragment error; done means the existing group's role is available to dependents without the reported JSIIError.

Written by the indexing model from the issue text.