Revise disconnected client error handling in WebFlux

A disconnected client error does not necessarily prevent us from setting
the status of the WebFlux ServerHttpResponse, which is only gated by a
committed flag and does not necessarily reflect the connection state.

This is why we need to check if we have a disconnected client error
first and handle it accordingly. We still set the response to 500
in case the disconnect client error is to a remote host in which
case it will propagate to the client.

Closes gh-36811

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -362,15 +362,14 @@ private Mono<Void> handleUnresolvedError(
 		ServerHttpResponse response = exchange.getResponse();
 		String logPrefix = exchange.getLogPrefix();
 
-		// Sometimes a remote call error can look like a disconnected client.
-		// Try to set the response first before the "isDisconnectedClient" check.
-
-		if (response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR)) {
-			logger.error(logPrefix + "500 Server Error for " + formatRequest(request), ex);
+		if (disconnectedClientHelper.checkAndLogClientDisconnectedException(ex)) {
+			// Attempt to send 500 in case of onward (rather than client) connection issue
+			response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR);
+			observationContext.setConnectionAborted(true);
 			return Mono.empty();
 		}
-		else if (disconnectedClientHelper.checkAndLogClientDisconnectedException(ex)) {
-			observationContext.setConnectionAborted(true);
+		else if (response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR)) {
+			logger.error(logPrefix + "500 Server Error for " + formatRequest(request), ex);
 			return Mono.empty();
 		}
 		else {