RFR(JDK 13/java.xml) 8180901: Transformer.reset() resets the state only once

[Joe Wang]

Please review a quick fix for preserving the initial state of the 
Transformer. The faulty impl passes a reference of the initial property 
setting to the working copy during reset, thus causes it to be altered 
by an user setting. Further reset would then no longer be able to return 
to the initial state.

JBS: https://bugs.openjdk.java.net/browse/JDK-8180901
webrevs: http://cr.openjdk.java.net/~joehw/jdk13/8180901/webrev/
Thanks,
Joe