zink: force line strip out when emulating stipple

zink: force line strip out when emulating stipple

Fixes a bug where, whenever a primtiive that has more than 2 vertices is rendered
with line stipple, the edge between the first and last vertex will have
stretched out stipple.

This happens because interpolation will occur between two non consecutive
stipple counters for the last edge
(which is between the last and first vertices).

Forcing `nir_create_passthrough_gs` to generate a line strip avoids
this because the last vertex will be duplicated and will have
the correct stipple counter for each edge.

Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21238>