8042889: (props) Properties.loadFromXML/storeToXML should consistently use the UKit parser

[Alan Bateman]

In JDK 8 we brought in a tiny XML parser to support the Properties 
loadFromXML/storeToXML methods. We needed this for the Compact Profiles 
work, specifically builds of compact1 as they do not have JAXP/XML APIs.

At the time we were a bit nervous about switching the XML parser for 
anything other than compact1 builds. One reason for this was that the 
original javadoc didn't constrain the encodings that has to be 
supported, another reason was confidence in the tests as we didn't have 
too many tests for these methods in the jdk repository.

I'd like to revisit one and switch over the implementation to always use 
the small parser. This allows for some clean-up, specifically it removes 
the need for the JDK-internal service type that was needed to use the 
JAXP code. On the original concerns then the spec was clarified in 8 to 
only require UTF-8 and UTF-16. In addition there were several tests 
added to better exercise these methods and the implementation. Also I 
think switching this early in JDK 9 means that we maximize the time to 
hear about any issues.

The webrev with the proposed changes is here, mostly red=removal so easy 
to review:

http://cr.openjdk.java.net/~alanb/8042889/webrev/

-Alan.