* GH-3502: More refactoring to avoid reflection
Fixes https://github.com/spring-projects/spring-integration/issues/3502
* Move `ChannelInitializer` bean registration into an `AbstractIntegrationNamespaceHandler` -
it was never used for annotations and Java DSL...
* Rework `IntegrationFlows.fromSupplier()` to call a provided `Supplier` directly -
not via reflection in the `MethodInvokingMessageSource`
* Resolve new Sonar smells
* Rework `EndpointSpec` to accept an expected factory bean instance via ctor arg
instead of reflection
* Rework `Jackson2JsonObjectMapper` to use well-known module instances directly -
not via reflection from their class names
* * Revert `DefaultMethodInvokingMethodInterceptor.methodHandleCache` property definition wrap
3f0c57894b