Validate that inline policy names of an IAM resource are unique

[jpb]

CloudFormation will not produce an error if two inline policies of an IAM Role (or user or group?) are the same. When the resource is created, only one of the policies will be applied to the resource, and which policy that gets applied will not be deterministic. Validate that inline policies of an IAM resource have unique names.

Policies can be attached via the Policies property of a resource or via a separate AWS::IAM::Policy which references the resource.