RFR [14/java.xml] 8230814: Enable SAX ContentHandler to handle XML Declaration

[Joe Wang]

Please review a new method addition to SAX ContentHandler that allows a 
SAX parser to send back information about the declaration of the input 
document.

JBS: https://bugs.openjdk.java.net/browse/JDK-8230814

CSR: https://bugs.openjdk.java.net/browse/JDK-8230824

webrev: http://cr.openjdk.java.net/~joehw/jdk14/8230814/webrev/

Thanks,
Joe