Fix doclint warngins in the java.xml package.
Many method definitions in interfaces and classes of the java.xml package are missing return, throws and param statements.
Add the missing return, throws and param statements.
Please see the attached diff and webrev for the added javadoc changes. For convenient references, please see: spediff: http://cr.openjdk.java.net/~joehw/jdk16/8251561/specdiff_01/overview-summary.html