render entirely unknown blocks in the plan output

[jbardin]

An unknown block can happen when using an unknown for_each value in a dynamic block assignment. The plan renderer was missing a check for entirely unknown blocks, causing them to be omitted from the human readable output.

The output with an unknown nested block previously looked like:

  # terraform_data.b will be created
  + resource "terraform_data" "b" {
      + id = (known after apply)
    }

And the updated output would be

  # terraform_data.b will be created
  + resource "terraform_data" "b" {
      + id = (known after apply)

      + nested (known after apply)
    }

Fixes #34933

[github-actions]

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[github-actions]

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