debt: refactor `terraform/resources.go.ConvertState` function

[ConvertState](https://github.com/coder/coder/blob/main/provisioner/terraform/resources.go) has been organically appended to over the last months/years and is now a 1k line monstrosity. Skimming through the function it appears a lot of looping is duplicated work and it's become quite difficult to read. It could use some love in being refactored with a control flow that's easier to flow.

Start with provisioner/terraform/resources.go and read the ConvertState function end to end, noting the repeated looping and how state is transformed. Preserve the current behavior while restructuring the function into a clearer control flow, then verify that the refactor remains behaviorally equivalent.

Scritto dal modello di indicizzazione a partire dal testo della issue.