Stream-out as point list for vs-out draws to get vertex reuse

* For vertex shader output only, we do the streamout as a point list and
  render each vertex once then we can reuse the same(ish) index buffer and
  topology as the original draw.
* For GS/DS out there will likely be some expansion of verts so we do the
  same as we used to.
Handle vtx highlights outside UI, for complex topologies. Refs #85