Fix doclint warnings in the java.xml package

Summary

Fix doclint warngins in the java.xml package.

Problem

Many method definitions in interfaces and classes of the java.xml package are missing return, throws and param statements.

Solution

Add the missing return, throws and param statements.

Specification

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

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