Introduce `SmartHttpMessageConverter`

[sdeleuze]

SmartHttpMessageConverter adresses several GenericHttpMessageConverter limitations, while providing a contract more consistent with WebFlux Encoder and Decoder, with the following differences:

• A ResolvableType parameter is used instead of a Type one.
• The source (MethodParameter today, maybe KType tomorrow) can be retrieved via the ResolvableType source.
• No contextClass parameter (can be deduced from the MethodParameter).
• A @Nullable Map<String, Object> hints additional parameter for write and read methods.