+str,htc #16071, #16072 New Stream Tcp and Http API

* StreamTcp and Http extensions now return Flows and Sources that can be materialized later
* Flow can now be completed with another flow to be turned into a runnable flow
* Java side of things is missing so tests will fail
While this is nice, I’d like to just try on the alternative for size:
~~~scala
Flow[Int].filter(_ % 2 == 1).map(_ * 10)
~~~