Add java jacoco coverage support

[ColdMacaroni]

This is something I pulled together in a couple hours. Only tested with a jacocoTestReport.xml file generated by the gradle plugin. Added some options to configure stuff.

Uses https://lunarmodules.github.io/luaexpat/ to parse XML. I tried to use lua-xmlreader but i could not get it to compile on my computer.

I'm leaving this PR as a draft because I don't really have the time to write the docs and make sure everything is working correctly and like up to spec, but it's functional enough that I think it's worth sharing. Hopefully I can tidy up the code a little and actually write docs once i can find some time, but if anyone feels like writing fixes and such that'd be really cool i think. I haven't seen any glaring errors tho,

(a little unrelated but i really like this plugin's approach to extensibility :saluting_face:)