Now cut lines detect vertices that they pass (almost) exactly over
and snap to them, to avoid making verts vert close to other ones.
Added radius arg to BKE_bmbvh_ray_cast so that can detect an obscuring
face when the ray might otherwise go exactly between two triangles.
Needed an isect_line_tri_epsilon function for similar reason.
Fixes last part of bug #35002. Other knife bugs still present but
getting this commit in now before continuing bug fixing.