* GH-8626: Provide cleaner `transform()` DSL
Fixes https://github.com/spring-projects/spring-integration/issues/8626
* Add missed `transform(String beanName, @Nullable String methodName)` API
* Introduce a `TransformerSpec` to expose a strict API to configure
transformer variants.
* Introduce `transformWith(Consumer<TransformerSpec>)` as a single point
of all possible transformer and its endpoint options
* Deprecate those `IntegrationFlowDefinition.transform()` variants
which are harder to configure as several lambda arguments
This change will make Kotlin & Groovy DSL more readable and straightforward
* * Use new `transformWith()` in tests where a deprecated API still used
* Add JavaDocs to `TransformerSpec`
* Fix generic types for `BaseIntegrationFlowDefinition.transformWith()` -
they make sense exactly on the `TransformerSpec.transformer()` only
* Apply `transformWith()` for Groovy DSL
* Introduce a new `ClassUtils.isLambda(Object candidate)`
and add a check for Groovy `Closure`
* Fix `GroovyIntegrationFlowDefinition.createConfigurerIfAny()` to propagate a `Consumer` argument
down to the `Closure`
* * Rename `TransformerSpec -> TransformerEndpointSpec` for better context
meaning of the class
* Introduce `KotlinTransformerEndpointSpec` as an extension of the `TransformerEndpointSpec`
to have an `inline fun <reified P> transformer(crossinline function: (P) -> Any)`
for Kotlin style
* Add `KotlinIntegrationFlowDefinition.transformWith(KotlinTransformerEndpointSpec)`
* Deprecate Kotlin methods which are covered by the mentioned `transformWith()`
* Fix tests to use new API
* Mentioned the change in the doc
070c1c6e60