topdown.RegisterBuiltinFunc Doesn't provide standardized error wrapping

[patrick-east]

Expected Behavior

When registering a builtin with the older topdown.RegisterFunctionalBuiltinX helpers the returned error is always checked and wrapped as needed with a topdown.Error. These errors have some nice additions like location info and a standard look/feel. All of the builtin functions should have error messages that have a similar look and feel.

Actual Behavior

The newer topdown.RegisterBuiltinFunc doesn't do any function wrapping, so any builtin functions that use it no longer get their errors wrapped unless they explicity return topdown.Error's with appropriate info.

The current result is that a there are a mix of error types returned by builtin functions and a user hitting errors will see different style of error messaging depending on the builtin.

Steps to Reproduce the Problem

{17:11} ~ ❯ cat /tmp/policy.rego
package foo

not_wrapped {
   net.cidr_expand(input.x)
}

wrapped {
   net.cidr_contains(input.x, "")
}
{17:11} ~ ❯ cat /tmp/input.json
{"x": 123}
{17:11} ~ ❯ opa eval -d /tmp/policy.rego -i /tmp/input.json 'data.foo.wrapped'
{
  "errors": [
    {
      "message": "net.cidr_contains: operand 1 must be string but got number",
      "code": "eval_type_error",
      "location": {
        "file": "/tmp/policy.rego",
        "row": 8,
        "col": 4
      }
    }
  ]
}
{17:11} ✘ ~ ❯ opa eval -d /tmp/policy.rego -i /tmp/input.json 'data.foo.not_wrapped'
{
  "errors": [
    {
      "message": "operand 1 must be string but got number"
    }
  ]
}

Additional Info

We should still be able to wrap the function call like we are doing now to normalize the error type returned.