47a5ebfde6
Commit d7970e4ab8 introduced support for JAXBElement in
Jaxb2XmlEncoder's encodeValue() method; however, canEncode() still
returned false for a JAXBElement element type.
This commit revises canEncode() so that it returns true for an element
type that is assignable from JAXBElement.
See gh-30552
See gh-32972
Closes gh-32977