Fix Jaxb2TypeScanner to scan for @XmlRegistry

Update ClassPathJaxb2TypeScanner to scan for @XmlRegistry classes.

Prior to this commit explicitly configured @XmlRegistry annotated classes
were not registered with the JAXBContext when using the 'packagesToScan'
property of the Jaxb2Unmarshaller.

Issue: SPR-10714
Merge pull request #324 from bijukunjummen/SPR-10714

# By Biju Kunjummen
* SPR-10714:
  Fix Jaxb2TypeScanner to scan for @XmlRegistry