Support CloudFormation Mappings

_this issue was extracted from the follow-up tasks of #1123_

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Could be converted to Terraform Locals with a constant value. Refer [here](https://github.com/aws/aws-cdk/blob/7966f8d48c4bff26beb22856d289f9d0c7e7081d/packages/%40aws-cdk/cloudformation-include/test/test-templates/functions-and-conditions.json#L2) for an example.