addrs: Reference.DisplayString method
addrs: Reference.DisplayString method

We've ended up implementing something approximately like this in a few
places now, so this is a centralized version that we can consolidate on
moving forward, gradually removing that duplication.

tommynsong/terraform,rnaveiras/terraform,hashicorp/terraform,rnaveiras/terraform,rnaveiras/terraform,hashicorp/terraform,tommynsong/terraform,hashicorp/terraform,tommynsong/terraform