message: Introduce Util::group_by()
diff: @@ -39,4 +39,14 @@ namespace vcpkg::Util
  {
  return std::find_if_not(cont.cbegin(), cont.cend(), pred);
  }
  +
  + template<class K, class V, class Container, class Func>
  + void group_by(const Container& cont, std::map<K, std::vector<const V*>>* output, Func f)
  + {
  + for (const V& element : cont)
  + {
  + K key = f(element);
  + (*output)[key].push_back(&element);
  + }
  + }
  }
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