Polish ExecutorSubscribableChannel

Consolidate inner classes used to invoke a subscriber with
interceptors.
Add MessageHandlingRunnable

Issue: SPR-12272
Allow configuring custom ThreadPoolTaskExecutor

Issue: SPR-12272
Create a builder for Jackson ObjectMapper

Jackson2ObjectMapperBuilder now allows to create ObjectMapper and XmlMapper
instances easily thanks to its fluent API.

This builder is used in Jackson message converters and views to instantiate default
ObjectMapper and XmlMapper.

This commit also add a createXmlMapper property to
Jackson2ObjectMapperFactoryBean in order to allow to create easily a XmlMapper
instance.

Issue: SPR-12243
Set Jackson FAIL_ON_UNKNOWN_PROPERTIES property to false by default

Issue: SPR-11891
Set Jackson DEFAULT_VIEW_INCLUSION property to false by default

Issue: SPR-12179
Improve @JsonView reference documentation

Issue: SPR-12270