DOM Reorganization: move IDOM from src/xercesc/idom to src/xercesc/dom and src/xercesc/dom/impl.  And rename IDOM_XXXX to DOMXXX.


git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@173726 13f79535-47bb-0310-9956-ffa450edef68