draw: use correct output prim for non-adjacent topologies in prim assembler.

draw: use correct output prim for non-adjacent topologies in prim assembler.

The decomposition done in the prim assembler will turn tri fans into tris,
but this wasn't reflected in the output prim type. Meaning with a tri fan
with 6 verts input, the output was a tri fan with 12 vertices instead of a
tri list with 12 vertices (not as bad as it sounds, since the additional tris
created would all be degenerate since they'd all have two times vertex zero
but still bogus).
This is because the prim assembler is used if either the input topology is
something with adjacency, or if prim id needs to be injected, and for the
latter case topologies without adjacency can be converted to basic ones.
Unfortunately decomposition here for inserting prim ids is necessary, at
least for the indexed case where we can't just insert the prim id at the
right place depending on provoking vertex.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>