Loop triangles are tessellated triangles create from polygons, for renderers
or exporters that need to match Blender's polygon tesselation exactly. These
are a read-only runtime cache.
Tessfaces are a legacy data structure from before Blender supported n-gons,
and were already mostly removed from the C code.
Details on porting code to loop triangles is in the release notes.
Differential Revision: https://developer.blender.org/D3539
e65784a051