code: @CheckReturnValue
      @BackpressureSupport(BackpressureKind.FULL)
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Flowable<T> retryUntil(final BooleanSupplier stop) {
          ObjectHelper.requireNonNull(stop, "stop is null");
          return retry(Long.MAX_VALUE, Functions.predicateReverseFor(stop));
      }
docs: Retries until the given stop function returns true.
  <dl>
  <dt><b>Backpressure:</b></dt>
  <dd>The operator honors downstream backpressure and expects the source {@code Publisher} to honor backpressure as well.
  If this expectation is violated, the operator <em>may</em> throw an {@code IllegalStateException}.</dd>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code retryUntil} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  @param stop the function that should return true to stop retrying
  @return the new Flowable instance