Exposes supported mime types in Jaxb2Decoder

Closes gh-23278

Author: rstoyanchev

spring-web/src/main/java/org/springframework/http/codec/xml/Jaxb2XmlDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -82,6 +82,10 @@ public Jaxb2XmlDecoder() {
 		super(MimeTypeUtils.APPLICATION_XML, MimeTypeUtils.TEXT_XML);
 	}
 
+	public Jaxb2XmlDecoder(MimeType... supportedMimeTypes) {
+		super(supportedMimeTypes);
+	}
+
 
 	/**
 	 * Configure a processor function to customize Unmarshaller instances.