!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
```java
boolean bindFailed;
try {
  Await.result(serverFuture2, FiniteDuration.create(5, TimeUnit.SECONDS));
} catch (BindFailedException e) {
  bindFailed = true;
}
assertTrue("Expected BindFailedException, but nothing was reported", bindFailed);
```