This commit introduces a new AbstractReactiveWebInitializer in
spring-web that relies on WebHttpHandlerBuilder to detect request
processing infrastructure beans from an ApplicationContext.
This eliminates the need to create a DispatcherHandler, since it is
expected to be a Spring bean, and as a result the initializers in
spring-webflux have been deprecated.
Issue: SPR-16144
Extract WebClient content into a separate file that is now included
both in the WebFlux and in the Integration sections.
This allows having RestTemplate and WebClient documented in one place
under Integration while also keeping the same included in the WebFlux
section too.
This change allows much more usable TOC for the reactive
stack and will make WebFlux documentation easier to
contribute thanks to a clearer split between both stacks.
Issue: SPR-15149