This commit updates CORS support in order to check Origin header
in CorsUtils#isPreFlightRequest which does not change how Spring
MVC or WebFlux process CORS request but is more correct in term
of behavior since it is a public API potentially used in another
contexts.
It also removes an unnecessary check in
AbstractHandlerMethodMapping#hasCorsConfigurationSource and processes
every preflight request with PreFlightHandler.
Closes gh-24327
bc7d010485