This commit introduces an abstraction that allows to convert HTTP
inputs to a data type based on a set of HttpMessageConverter.
Previously, the AssertJ integration was finding the first converter
that is able to convert JSON to a Map (and vice-versa) and used that
in its API. With the introduction of SmartHttpMessageConverter, exposing
a specific converter is fragile.
The added abstraction allows for converting other kind of input than
JSON if we need to do that in the future.
Closes gh-33148
4bdb772d39