SseEmitter support for multiline String

Closes gh-30965

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitter.java

@@ -237,6 +237,9 @@ public class SseEmitter extends ResponseBodyEmitter {
 		public SseEventBuilder data(Object object, @Nullable MediaType mediaType) {
 			append("data:");
 			saveAppendedText();
+			if (object instanceof String text) {
+				object = StringUtils.replace(text, "\n", "\ndata:");
+			}
 			this.dataToSend.add(new DataWithMediaType(object, mediaType));
 			append('\n');
 			return this;