The spring.jackson.read and spring.jackson.write properties are
JSON-specific. To make this more clear, this commit moves them
beneath spring.jackson.json. This also paves the way for
spring.jackson.cbor and spring.jackson.xml properties for CBOR- and
XML-specific settings should we add auto-configuration for XMLMapper
and/or CBORMapper in the future.
Closes gh-47328
Prior to this commit, Spring Boot would use Framework's
`Jackson2ObjectMapperBuilder` to configure the `ObjectMapper` instance.
This builder would configure the `ProblemDetail` mixin automatically.
With the introduction of Jackson 3.x support, Spring Framework removed
its builder in favor of the native Jackson builder. As a result, the
mixin is not registered with the `JsonMapper` aymore.
This commit ensures that the mixin is registered if the `ProblemDetail`
class is present in the classpath.
Closes gh-47298
Andy Wilkinson
Brian Clozel
Moritz Halbritter
Phillip Webb