JDK 20, foreign-abi

Finally updated the foreign-abi branch of nativez, zcl, and jjmpeg to the OpenJDK 20 API for foreign native access. It's very much untested and probably buggy but it compiles and a few things run so it should be on the right track at least.

Most of the changes were pretty straightforward and some of the API changes simplified a few things.

It was mostly a learning exercise to find out what has changed in the API but I thought I may as well do them all at the same time. I'm sort-of more interested in vulkanz but it's been so long since I worked on it I've forgotten where I was at. So maybe i'm not that much interested in it!