Provide proper licenses for contrib/java/xml-apis/xml-apis
`SAX-PD` stands for
```
SAX is free!
In fact, it's not possible to own a license to SAX, since it's been placed in the public domain.
```
(full text is available [here](http://www.saxproject.org/copying.html)).
`W3C-19980720` text can be found [here](https://spdx.org/licenses/W3C-19980720.html).
thegeorg