Netty 4.1 Optimizations

[franz1981]

These changes are partially related https://redhatperf.github.io/post/type-check-scalability-issue/ and are mostly
limits of the JDK platform (still to be addressed, see https://bugs.openjdk.org/browse/JDK-8180450).

Said that, luckly, they can be fixed in user code easily and these are the changes addressing both proper scalability issue(s) and inefficient handling of type check (while an interface type is not implemented by a concrete type).

The changes are saving:

• DefaultHttpRequest instanceof HttpResponse on HttpObjectDecoder::isContentAlwaysEmpty
• DefaultFullHttpResponse instanceof HttpRequest on HttpResponseEncoder::acceptOutboundMessage
• LastHttpContent.EMPTY_LAST_CONTENT instanceof HttpRequest on HelloServerHandler::channelRead
• DefaultHttpRequest instanceof ReferenceCounted on ReferenceCountUtil.release's (still in HelloServerHandler::channelRead)

While there's another one that cannot be fixed here, but it will be in Netty, directly:

• Avoid slow type checks against promises on outbound buffer's progress netty/netty#13225 on Netty 4.1.90.Final

This PR is bumping to the latest Netty release and its io_uring incubator as well.