Blender 3.5 moved edge sharp to a generic attribute and 3.6 moved face
smooth to a generic attribute. The old API still works for now, but is
slower and may be removed in 4.0, so this patch updates FBX IO to use
the new "sharp_edge" and "sharp_face" attributes.
Because the old API was face smooth, not sharp, the logic for working
with "sharp_face" is inverted compared to before.
When the "sharp_edge" or "sharp_face" attributes do not exist, all edges
or faces can be assumed to not be marked sharp, reducing necessary work.
A comment comparing the speed of calculating polygon sides from `t_ls`
vs getting polygon sides from polygon "loop_total" has been updated to
reflect the change that "loop_total" is not stored internally as of 3.6
and is now slower to access.
This patch makes a minor change to the import of FBX files, whereby code
that used to set every face to smooth now removes the "sharp_face"
attribute instead.