1. Update the HandlerMapping contract to state that CORS checks are expected
to be applied before returning a handler.
2. DispatcherHandler checks explicitly for pre-flight requests or CORS failed
requests and skips handling for both. Technically no change since
AbstractHandlerMapping already returns a NO_OP_HANDLER for those cases.
The purpose however is for the DispatcherHandler to also guarantee more
explicitly that no such handling can take place for such cases.
As one consequence, this makes it possible to invoke the DispatcherHandler from
anywhere in the WebFilter chain in order to "handle" a pre-flight request, and
then skip the rest of the WebFilter chain.
See gh-26257
95752ef1c9