This commit changes the `HandlerStrategies` builder to use
`ServerCodecConfigurer` for configuring Decoder|Encoder and
HttpMessage[Reader|Writer]. Note that the configurer is not exposed
directly, but wrapped so that `HandlerStrategies` can keep on returning
`this` for a proper builder pattern.
This commit also removes the HandlerStrategies methods that take an
application context, as it was too naive approach to simply look up
every message reader and writer in the context.
Issue: SPR-15415