!str #16400 Add Java API for StreamTcp

* move io.StreamTcp to scaladsl.StreamTcp
* add javadsl.StreamTcp that delegates to scaladsl implementation
* move impl
* add java test
maybe I’m stupid or Eclipse lies to me, but I cannot find any use of `ConnectionAttemptFailedException`, it seems to be a remnant. If you can confirm this, then go ahead and just axe it.