Simplify ability to get state JSON from state affecting subcommands

[paultyng]

Here is the upstream issue to simplify this interaction: hashicorp/terraform#25467

Ideally we would be able to do something like terraform apply -state-out-json foo.json and just read that file with the terraform-json module. We could then use this in the methods to return the state (ie. Apply(...) (*tfjson.State, error))