Ability to write to Terraform UI from resource

Currently it looks like impossible to write any kind of text to the CLI from TF resource during read/update/delete/etc function. As it doesn't receive `terraform.UIOutput`

This block's me from the proper AWS ECS Service deployment implementation (where we're waiting for the successful deployment).

This also might be really useful for any resource that has complicated create/delete/update process so it's useful to show some information about the process to the user.

TF version: 0.11.7

Start by tracing the resource Read, Update, and Delete entry points and how terraform.UIOutput is currently exposed to them. Determine the intended way for a resource to report progress during long operations; done means resource implementations can write useful status text without breaking provider behavior.

Written by the indexing model from the issue text.