WIP: Nested Sorting

[kamilkisiela]

#3737

Given this schema:

type Country @entity {
  id: ID!
  capital: City!
  cities: [City!]!
}

type City @entity {
  id: ID!
  name: String
  population: Int
  landmarks: [String!]!
}

It adds fields of child entity to *_orderBy enum:

enum Country_orderBy {
   id
   capital
   cities
+  capital__id
+  capital__name
+  capital__population
}

• [x] sort by type Child @entity { name: String }
• [x] can't sort by type Child @entity { names: [String] }
• [x] can't sort by type Child @entity { secondLevelChild: AnotherEntity }
• [x] can't sort by type Child @entity { secondLevelChildren: [AnotherEntity] }
• [x] support @derivedFrom
• [x] sort by interface Child { name: String }
• [ ] sort interface by type Child @entity { name: String }