Ensure correct array elements order in Jackson2JsonEncoder

Issue: SPR-14586

Author: sdeleuze

spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java

@@ -96,7 +96,7 @@ public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory buffe
 		Mono<DataBuffer> endArray = Mono.just(bufferFactory.wrap(END_ARRAY_BUFFER));
 
 		Flux<DataBuffer> array = Flux.from(inputStream)
-				.flatMap(value -> {
+				.concatMap(value -> {
 					DataBuffer arraySeparator = bufferFactory.wrap(SEPARATOR_BUFFER);
 					return Flux.just(encodeValue(value, bufferFactory, elementType), arraySeparator);
 				});