terraform_unused_declarations: Add support for scoped data sources

[wata727]

See also https://developer.hashicorp.com/terraform/language/checks

Terraform v1.5 now supports check blocks and scoped (nested) data sources.
This PR adds support for them to the terraform_unused_declarations rule.

[wata727]

Note: This logic is broken if scoped data source addresses are unique in check blocks.

As far as I've looked, this logic is valid because in v1.6.0 it's unique in the module.

data "http" "terraform_io" {
  url = "https://www.terraform.io"
}

check "health_check" {
  data "http" "terraform_io" {
    url = "https://www.terraform.io"
  }

  assert {
    condition = data.http.terraform_io.status_code == 200
    error_message = "${data.http.terraform_io.url} returned an unhealthy status code"
  }
}

@wata727 ➜ /tmp $ terraform validate
╷
│ Error: Duplicate data "http" configuration
│
│   on main.tf line 6, in check "health_check":
│    6:   data "http" "terraform_io" {
│
│ A http data resource named "terraform_io" was already declared at main.tf:1,1-27. Resource names must be unique per type in each module, including within check
│ blocks.