getindices() should return the positional index from a list

As of 3.9.0 getindices() always returns a list. If it's called on a non-existant or undefined variable it returns an empty list.

Currently (as of 3.12.x) getindcies() when called on a list returns an empty list.

I think it would be more useful if getindices() when called on a list, returns the positional index of the elements.

For example:

bundle agent main
{
   vars:
      "list" slist => { "beta", "alpha", "gamma" };
      "list_index" slist => sort( getindices( list ), lex );
      "list_values" slist => sort( getvalues( list ), lex);

   reports: 
      "List index:";
      "$(list_index)";
      "List values:";
      "$(list_values)";
}

This outputs:

R: List index:
R: List values:
R: alpha
R: beta
R: gamma

I think it should output:

R: List index:
R: 0
R: 1
R: 2
R: List values:
R: alpha
R: beta
R: gamma