fix(misconf): handle of unresolvable values in checks

[nikpivkin]

If the value is equal to cty.NilVal (for terraform configurations) or is unknown, it is marked as unresolvable. Methods that check conditions return false if the value is unresolvable. For example, calling the Empty method for an unresolvable empty string will return false, and calling the EqualTo method with an argument of 0 for an unresolvable number 0 will also return false. This helps avoid false positives when the value is unknown. Example of a configuration where the kms_master_key_id attribute is unknown because it references an attribute from a data block:

data "aws_kms_alias" "test" {
  name = "alias/aws/s3"
}

resource "aws_sns_topic" "test" {
  name = "user-updates-topic"
  kms_master_key_id = data.aws_kms_alias.test.target_key_id
}

Rego checks should use functions that take into account handling of unresolvable values instead of directly accessing them.

Discussed in #7760