Support multi-part ranges for `terraform_version`

I'd like to be able to set multi-part ranges for `terraform_version` (e.g. `terraform_version: >= 1.3.3, != 1.3.4`) which is supported in Terraform but doesn't currently work in this action.

Start by tracing how the GitHub Action reads and validates the terraform_version input, then compare that handling with Terraform's multi-part range syntax. The work is done when examples such as ">= 1.3.3, != 1.3.4" are accepted and existing single-part version constraints continue to work.

Written by the indexing model from the issue text.