Pre-fuse http server layer (#20990)

* Ported the first pre-fuse part endre did in pr #1972

* Allow the same HttpServerBluePrint to materialize multiple times

HttpRequestParser now behave like a proper GraphStage (with regards to materialization)
HttpResponseParser is kept "weird" to limit scope of commit.

* TestClient method to dump with http client and curl in parallel for comparison

* Cleanup

* tightening down what can be overriden
* tightening down access modifiers
* updates according to review

* Better defaults for the test server

* Ups. Don't listen to public interfaces in test server by default.

akka-actor-tests/src/test/scala/akka/util/ByteStringSpec.scala

@@ -414,7 +414,7 @@ class ByteStringSpec extends WordSpec with Matchers with Checkers {
       def excerciseRecombining(xs: ByteString, from: Int, until: Int) = {
         val (tmp, c) = xs.splitAt(until)
         val (a, b) = tmp.splitAt(from)
-        (a ++ b ++ c) should ===(xs) 
+        (a ++ b ++ c) should ===(xs)
       }
       "recombining - edge cases" in {
         excerciseRecombining(ByteStrings(Vector(ByteString1(Array[Byte](1)), ByteString1(Array[Byte](2)))), -2147483648, 112121212)