Update API to not extend org.w3c.dom

[lukasj]

Currently the API is built as an extension to DOM (org.w3c.dom) API. With access restrictions to related implementation classes on JPMS (JDK 9+), this implies unnecessary requirement on the SOAP API implementation provider to also provide some implementation of the DOM API, since it is not guaranteed that DOM API implementation as such is extensible.

To remove this obstacle, the SOAP API should be changed in a way it is built on top of DOM API (instead of extending it).
In the other words this means removing extends org.w3c.dom.Node from jakarta.xml.soap.Node, extends org.w3c.dom.Element from jakarta.xml.soap.SOAPElement, extends org.w3c.dom.Text from jakarta.xml.soap.Text and changing jakarta.xml.soap.SAAJResult. Additional changes to existing interfaces might be required as well.

It would be also good idea to rename jakarta.xml.soap.Node and jakarta.xml.soap.Text so they don't hide existing DOM interfaces.