d3d12: Run point sprite lowering pass on multi-stream GS when safe

d3d12: Run point sprite lowering pass on multi-stream GS when safe

In the case of a multi-stream GS that is attempting to output wide
points to stream 0, we can support this by lowering stream 0 to
triangles and then removing the other streams. This is only valid
to do if the other streams are not being written to stream output,
either if they're not present in the SO info or no buffer is bound.

Fixes the arb_gpu_shader5/arb_gpu_shader5-emitstreamvertex_nodraw
piglit test which does this.

Reviewed-by: Sil Vilerino <sivileri@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14624>