Find a way to incorporate the Java Porter Stemmer

[martindholmes]

At various times I've come across a Java lib incorporating all the currently-supported languages from the Porter Stemmer project as well as a collection of JavaScript implementations. There are various sources for these, so identifying the most reliable and canonical versions would be the first step (for Java, presumably here: https://snowballstem.org/download.html). If we can find a way to wrap the Java lib so that Saxon can use it, and we can find matching JS implementations for all the languages, we may be able to replace our own stemmers and support many more languages.

[joeytakeda]

I did do a bit of this work a while back; I never ended up finishing it up, but might be a good base: https://github.com/joeytakeda/saxon-ext-test