chore(terraform): hook into evaluateStep behavior with custom hooks

[Emyrk]

Description

Let me know if I am missing some other means to make this work

evaluateStep handles many terraform semantics such as default values for 'variables'. A hook into these steps allows defining additional semantics, likely to mirror those of the actual provider implementation.

This must be done in evaluateStep, as things such as expandBlocks occur afterwards. Without this hook, the ExpandBlock must be called manually outside of the executor.

data "your_custom_data" "this" {
  default = ["a", "b", "c"]
}

data "random_thin" "that" {
  dynamic "repeated" {
    for_each = data.your_custom_data.this.value
    content {
      value = repeated.value
    }
  }
}

Conversation

Calling ExpandBlock outside is ok, however I wonder if calling EvaluateStep again is required in order to be correct. EvaluateSteps is called here after ExpandBlocks

https://github.com/aquasecurity/trivy/blob/main/pkg/iac/scanners/terraform/parser/evaluator.go#L145

Hence why this hook was added. To place similar semantic code to variable defaults in the same spot.

Checklist

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