Consider introducing `JacksonXmlDecoder` & friends

[tschut]

Spring Framework 7 migrated to Jackson 3. With this, Jackson2JsonDecoder got deprecated and is replaced by JacksonJsonDecoder.

However, contrary to what the name suggests, Jackson2JsonDecoder can be constructed with an arbitrary Jackson 2 ObjectMapper, which makes it support not only Json, but Xml (and other formats) just as well.

With the new JacksonJsonDecoder this is no longer possible, since it uses JsonMapper over ObjectMapper.

It would be nice (and ease migration to Spring Framework 7) if there was an equivalent JacksonXmlDecoder (and JacksonXmlEncoder obviously).

edit: some typos