There is a natural way to implement ServerHttpMessage[Reader|Writer]
from [Encoder|Decoder]HttpMessageWriter by resolving hints first via
a protected method and then delegating to the regular read or write.
There is no downside either since it does not prevent
[Encoder|Decoder]HttpMessageWriter from being used for both client and
server scenarios while they're more useful.
As a positive side effect AbstractServerHttpMessage[Reader|Writer] can
be removed further simplfications can be made (in a future commit) to
accept ServerHttpMessageWriter for configuration purposes on the server
side and remove instanceof checks for ServerHttpMessageWriter.
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