Bugfix/webflux Fix a support method logic of ServerResponseResultHandler .

[hongjunan]

org.springframework.web.reactive.function.server.support.ServerResponseResultHandler.java can NOT handle Mono<ServerResponse> or Flux<ServerResponse>.

public boolean supports(HandlerResult result) always return false.
because it check a returnValue type of HandlerResult .
need to replace a return type with a generic type of it.
see below error code.

	@Override
	public boolean supports(HandlerResult result) {
		return (result.getReturnValue() instanceof ServerResponse);
	}

fix like below
it has to compare with a generic type of returnType

	@Override
	public boolean supports(HandlerResult result) {
		return ServerResponse.class.isAssignableFrom(result.getReturnType().getGeneric().toClass());
	}

Related: https://github.com/spring-projects/spring-framework/issues/27266

[ascopes]

should this use .toClass().isAssignableFrom or .equals rather than class instance identity? (could see situations where this may be problematic in environments that use OSGi, for example).

[hongjunan]

should this use .toClass().isAssignableFrom or .equals rather than class instance identity? (could see situations where this may be problematic in environments that use OSGi, for example).

Totally agree with your comment.
i fixed it. thank you.

https://github.com/spring-projects/spring-framework/pull/27268/commits/8e2c3f0d44b1613db4453ed599b6f173caddbd33

[rstoyanchev]

We don't need both an issue and a PR, and typically, the issue is closed, but in this case the conversation is under way on the issue, and the PR is trivial. It can always be re-opened.