indices: add translate/generate functions for unfilled modes

indices: add translate/generate functions for unfilled modes

Most of the time unfilled rendering requires a lot more thought than
just translating triangles to lines or points.  But sometimes, you can
do exactly that, and it can be quite a bit quicker.  Add code to do the
translation.  The caller has to determine whether it's a legal thing
to do in the current state, in particular you'd need:
  - culling disabled
  - offset disabled
  - same front and back fill modes
  - possibly other stuff I can't think of.