static <T1, T2> Seq<Tuple2<T1, T2>> crossApply(Stream<? extends T1> stream, Function<? super T1, ? extends Stream<? extends T2>> function2) {
        return crossApply(seq(stream), t -> seq(function2.apply(t)));
    }
Cross apply 2 functions to a stream.
<p>
<pre><code>
// (tuple(1, 0), tuple(2, 0), tuple(2, 1))
Seq.of(1, 2).crossApply(t -> Seq.range(0, t))
</code></pre>
jOOL-java-8/src/main/java/org/jooq/lambda/Seq.java