code: public EntryStream<K, V> prepend(K key, V value) {
          return supply(new PrependSpliterator<>(spliterator(), new SimpleImmutableEntry<>(key, value)));
      }
docs: Returns a new {@code EntryStream} which is a concatenation of the
  supplied key-value pair and this stream.
  
  <p>
  This is a <a href="package-summary.html#StreamOps">quasi-intermediate
  operation</a> with <a href="package-summary.html#TSO">tail-stream
  optimization</a>.
  
  @param key the key of the new {@code Entry} to prepend to this stream
  @param value the value of the new {@code Entry} to prepend to this stream
  @return the new stream