RFR: 8152423: Generated temp files (+JXF...temp) for custom fonts not deleted on exit.

[Phil Race]

Please review :-
Bug : https://bugs.openjdk.java.net/browse/JDK-8152423
Fix : http://cr.openjdk.java.net/~prr/8152423/ 
<http://cr.openjdk.java.net/%7Eprr/8152423/>

"Release" was not being called on the DirectWrite font object
so it held a reference to the file, which on Windows prevents
the file from being deleted.

-phil