/**
   * Returns the index in {@code iterator} of the first element that satisfies the provided {@code
   * predicate}, or {@code -1} if the Iterator has no such elements.
   *
   * <p>More formally, returns the lowest index {@code i} such that {@code
   * predicate.apply(Iterators.get(iterator, i))} returns {@code true}, or {@code -1} if there is no
   * such index.
   *