code: @NotNull
      public <U> ComparatorCompat<T> thenComparing(
              @NotNull Function<? super T, ? extends U> keyExtractor,
              @NotNull Comparator<? super U> keyComparator) {
          return thenComparing(comparing(keyExtractor, keyComparator));
      }
docs: Adds the comparator, that uses a function for extract
  a sort key, to the chain.
  
  @param <U> the type of the sort key
  @param keyExtractor  the function that extracts the sort key
  @param keyComparator  the comparator used to compare the sort key
  @return the new {@code ComparatorCompat} instance