Allow non-literal expressions in module blocks

[radeksimko]

As reported in hashicorp/terraform-ls#620 prior to this patch, references would not be recognized within the module block, except for static/core attributes like count:

module "example" {
  source "..."
  foo = var.bar # HERE
}

This patch makes the module use the same the expression type generation logic we use for all other provider-specific attributes (applied to most attributes within provider, resource and data blocks).