Support generics in the JsonToObjectTransformer (#2819)

* Support generics in the `JsonToObjectTransformer`

* Deprecate `JsonObjectMapperAdapter` if favor of `default` methods in
the `JsonObjectMapper`
* Introduce `JsonObjectMapper.fromJson(Object, ResolvableType)` to
support generics during deserialization
* Add `JsonHeaders.RESOLVABLE_TYPE` header handling for the
`ResolvableType` management
* Add `ResolvableType` argument into the `JsonToObjectTransformer`
* Change the `JsonToObjectTransformer` logic to consult request message
headers first
* Add `ResolvableType`-based factory method into the `Transformers`
* Document the change

* * Use `0` for conversion to array for headers to remove
in the `JsonToObjectTransformer`

src/reference/asciidoc/transformer.adoc

@@ -449,6 +449,10 @@ See <<spel-property-accessors>> for more information.
 
 Beginning with version 5.1, the `resultType` can be configured as `BYTES` to produce a message with the `byte[]` payload for convenience when working with downstream handlers which operate with this data type.
 
+Starting with version 5.2, the `JsonToObjectTransformer` can be configured with a `ResolvableType` to support generics during deserialization with the target JSON processor.
+Also this component now consults request message headers first for the presence of the `JsonHeaders.RESOLVABLE_TYPE` or `JsonHeaders.TYPE_ID` and falls back to the configured type otherwise.
+The `ObjectToJsonTransformer` now also populates a `JsonHeaders.RESOLVABLE_TYPE` header based on the request message payload for any possible downstream scenarios.
+
 [[transformer-annotation]]
 ==== Configuring a Transformer with Annotations
 

src/reference/asciidoc/whats-new.adoc

@@ -16,6 +16,9 @@ See <<rate-limiter-advice>> for more information.
 [[x5.2-general]]
 === General Changes
 
+The `JsonToObjectTransformer` now supports generics for the target object to deserialize into.
+See <<json-transformers>> for more information.
+
 [[x5.2-amqp]]
 ==== AMQP Changes