Eliminate SAAJ dependency on JAXP internal API

java.xml currently exports a few qualified exports to java.xml.ws to use its internal API. java.xml.ws may be run as standalone that will not be able to access these internal APis unless --add-exports option is used to break in encapsulation.

This issue suggests to re-examine SAAJ use of JAXP internal APIs and determine if it's possible to eliminate its dependency of JAXP internals.
 
 com.sun.xml.internal.messaging.saaj.soap.SOAPDocumentFragment -> com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.SOAPDocumentFragment -> com.sun.org.apache.xerces.internal.dom.DocumentFragmentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.SOAPDocumentImpl -> com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.SOAPDocumentImpl -> com.sun.org.apache.xerces.internal.dom.DocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.CDATAImpl -> com.sun.org.apache.xerces.internal.dom.CDATASectionImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.CDATAImpl -> com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.ElementImpl -> com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.ElementImpl -> com.sun.org.apache.xerces.internal.dom.ElementNSImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.SOAPCommentImpl -> com.sun.org.apache.xerces.internal.dom.CommentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.SOAPCommentImpl -> com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.SOAPTextImpl -> com.sun.org.apache.xerces.internal.dom.CoreDocumentImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.soap.impl.SOAPTextImpl -> com.sun.org.apache.xerces.internal.dom.TextImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.util.ParserPool -> com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl java.xml (qualified)
   com.sun.xml.internal.messaging.saaj.util.ParserPool -> com.sun.org.apache.xerces.internal.util.SymbolTable java.xml (qualified)