RFR [16/java.xml] 8251561: Fix doclint warnings in the java.xml package

[Joe Wang]

Pelase review a patch to add the missing @return, @throws, @param 
statements in the java.xml package (excluding the DOM component).

JBS: https://bugs.openjdk.java.net/browse/JDK-8251561
CSR: https://bugs.openjdk.java.net/browse/JDK-8251995

webrev: http://cr.openjdk.java.net/~joehw/jdk16/8251561/webrev_01/

Thanks,
Joe