The WebSocketHander adapters are now neutral for client vs server-side
use with the adapters for RxNetty and Reactor Netty (server-side only)
completely removed.

A new HandshakeInfo carries information about the handshake including
URI, headers, and principal from the upgrade strategy, to the adapter,
and then to the session.

WebSocketSession exposes the HandshakeInfo as well reducing its overall
number of methods.