Deduplicate triangle-triangle intersection code

[Garrett-R]

I noticed there were 2 functions with nearly identical code. Two small differences:

1. the static version was slightly more performant having more ref usages, avoiding making copies. I took this one
2. the non-static one had a side-effect of setting the Type which I've maintained.

This is a pure refactor, API and functionality should be the same.

[Garrett-R]

I also added my project to the "Projects using g3Sharp" list, but let me know if you want me to drop that commit.