Allow value variables in facet filters

MichelDiz commented :

It seems reasonable to me. Value variables could come from other blocks and amplify the possibilities of querying.

{
  AB as var(func: anyofterms(name, "Alice Bob Charlie")) {
    value as math(5)
   }
  q(func: uid(AB)) {
    rated @facets @facets(eq(rating, val(value))) {
      uid
    }
  }
}

Update(2021): just fixed the query.