Add a properties setter to ProblemDetail

Mainly to allow Kotlin idiomatic properties assignment.

Closes gh-31430

spring-web/src/main/java/org/springframework/http/ProblemDetail.java

@@ -216,6 +216,18 @@ public class ProblemDetail {
 		this.properties.put(name, value);
 	}
 
+	/**
+	 * Setter for the {@link #getProperties() properties map}.
+	 * <p>By default, this is not set.
+	 * <p>When Jackson JSON is present on the classpath, any properties set here
+	 * are rendered as top level key-value pairs in the output JSON. Otherwise,
+	 * they are rendered as a {@code "properties"} sub-map.
+	 * @param properties the properties map
+	 */
+	public void setProperties(@Nullable Map<String, Object> properties) {
+		this.properties = properties;
+	}
+
 	/**
 	 * Return a generic map of properties that are not known ahead of time,
 	 * possibly {@code null} if no properties have been added. To add a property,