message: gather_non_load_strings in parallel for each dex
  Summary: Faster is better.
diff: @@ -66,10 +66,14 @@ void DedupStrings::run(DexStoresVector& stores) {
  // Compute set of non-load strings in each dex
  std::unordered_set<const DexString*> non_load_strings[dexen.size()];
  - for (size_t i = 0; i < dexen.size(); i++) {
  + auto wq = workqueue_foreach<size_t>([&](size_t i) {
  auto& strings = non_load_strings[i];
  gather_non_load_strings(dexen[i], &strings);
  + });
  + for (size_t i = 0; i < dexen.size(); i++) {
  + wq.add_item(i);
  }
  + wq.run_all();
  // For each string, figure out how many times it's loaded per dex
  ConcurrentMap<DexString*, std::unordered_map<size_t, size_t>> occurrences =
  